Handle errors on API when a project does not have a repository

Remember the project default tab for 30 days

Added support for firing system hooks on group create/destroy and adding...

Active users and logged in users

/cc @marc @haydn @dzaporozhets

See merge request !1443

Added tests and updated docs. Also adding 'user_id' field in the hooks for adding/removing user from team.

Improve web editor

* focus on web editor
* Make editor looks same for new and edit file
* Refactor editor JS
* Improved satellite logic for new files

See merge request !1441

File creation and editing refactored

* Refactored controllers/helpers/views related to blob resource
* make it possible to create new file in empty repository

Second step in building #1930

See merge request !1440

Bigger font-size for code browsing

See merge request !1439

Create first file from empty repository via UI. pt1

* Backend can now commit file to empty repository.
* Empty project UI has new file button

First step in building #1930

See merge request !1438

Redesign project avatar page

See merge request !1437

Notify participants on close or reopen of issue/mr

Fixes #1891

cc @sytse

See merge request !1436

Also refactor NotificationService a bit

Improve project icon UI

See merge request !1435

Remove default project icon

See merge request !1434