Abstract WebRTC signalling to prepare for ERP5,
detect client browser unloading and send message,
directly display URLs of images as an actual <img>,
add global "notifications" such as joining and /help,
clean names to avoid OAuth2 state conflicts in the URL,
make Dropbox authentication more robust against failures,
and parse non-image URLs as <a> using a regular expression.

Add initial files for space chat project. Features include:
- Real-time text-based communication system over WebRTC
- Modular chat separation into 'folders' and 'rooms'
- Multiple signalling options, including text or Dropbox
- Configurable local storages like IndexedDB using jIO
- Follows WebRTC best practices by using adapter.js shim
- Adjustable polling behaviour for managing Dropbox offers
- Powerful offline synchronization algorithms within rooms

Actually none of the above are even features, this chat is very bad.

The file list is:
- adapter.js: shim for cross-browser WebRTC compatibility
- fast_priority_queue.js: by adamhooper, for sorting messages
- gadget_erp5_chat: main chat gadget, contains local storage and login
- gadget_erp5_chat_login: gadget to get name, folder, and room from user
- gadget_erp5_chat_webrtc: WebRTC signalling gadget to open communications
- gadget_erp5_chat_panel: actual chat gadget, has all the chatting functions

MonthlyRangeMovementGroup: make tested property list configurable, whose default is ('start_date', 'stop_date').

Fix inconsistencies from gadgets

/cc @jerome 

/reviewed-on nexedi/erp5!225

erp5_knowledge_pad: Fix inconsistency with preferred_height and preferred_width in google_maps gadget

ERP5Type.ConsistencyMessage for PropertyTypeValidity type_check on portal_gadgets/google_maps (message: Attribute preferred_width should be of type string but is of type <type 'int'>)
ERP5Type.ConsistencyMessage for PropertyTypeValidity type_check on portal_gadgets/google_maps (message: Attribute preferred_height should be of type string but is of type <type 'int'>)

erp5_knowledge_pad: Fix inconsistency with preferred_height and preferred_width in google_calendar gadget

ERP5Type.ConsistencyMessage for PropertyTypeValidity type_check on portal_gadgets/google_calendar (message: Attribute preferred_width should be of type string but is of type <type 'int'>)
ERP5Type.ConsistencyMessage for PropertyTypeValidity type_check on portal_gadgets/google_calendar (message: Attribute preferred_height should be of type string but is of type <type 'int'>)

erp5_knowledge_pad: Fix inconsistency with preferred_height and preferred_width in google_search gadget

ERP5Type.ConsistencyMessage for PropertyTypeValidity type_check on portal_gadgets/google_search (message: Attribute preferred_width should be of type string but is of type <type 'int'>)
ERP5Type.ConsistencyMessage for PropertyTypeValidity type_check on portal_gadgets/google_search (message: Attribute preferred_height should be of type string but is of type <type 'int'>)

ERP5Type.ConsistencyMessage for PropertyTypeValidity type_check on portal_gadgets/clock (message: Attribute preferred_width should be of type string but is of type <type 'int'>)
ERP5Type.ConsistencyMessage for PropertyTypeValidity type_check on portal_gadgets/clock (message: Attribute preferred_height should be of type string but is of type <type 'int'>)

erp5_payroll_l10n_fr: reflects change in entreprise/employer from paysheets into the dialog aggregating paysheets for DSN social reports

/reviewed-on nexedi/erp5!229

erp5_calendar: Leave Request Period only use services as Resource

erp5_travel_expense: In expense report, remove useless rsvp.queue, do not overwrite special character

synchronize automatically data block web site

A Localisation Record is created when submit a expense record
only one received localisation record per user

erp5_travel_expense: localisation search should not prevent image preview

erp5_travel_expense: make sure localisation gadget is loaded

erp5_travel_expense: don't create localisation record when location is undefined

erp5_travel_expense: naming convention

erp5_travel_expense: Have Projects availables in Expense, define group on images and set source_section

epr5_payroll: update social_declaration view as transactions can be aggregated by several social declarations

It will allow to differenciate the Employer for which the Employee is working, and the Company to which the accounting and the payment are related

This reverts commit 6b6f1fe0.