Ensure a new subgadget is declared when the panel is opened

Editor panel can be closed from the sort/filter buttons

Localization should be done by fetching the locales and provide it as parameter to toLocaleDateString.

Fixes: UnboundLocalError: local variable 'translated_portal_type' referenced before assignment

in ready step, indexeddb storage is not yet create, so translation gadget can't get
language setting

in ready step, indexeddb storage is not yet create, so translation gadget can't get
language setting

This fixes number of Jupyter bugs.

Tests passing here: 

https://nexedi.erp5.net/test_result_module/20161117-147BEEA9

/reviewed-on nexedi/erp5!198

Same as for commit c3450f14:
BTrees don't accept None as key anymore.

Traceback (most recent call last):
  File "Products/ERP5/tests/testAuthenticationPolicy.py", line 538, in test_05_HttpRequest
    self.assertFalse(person.isLoginBlocked())
  File "Products/ERP5/mixin/login_account_provider.py", line 68, in isLoginBlocked
    return method(**kw)
  File "ZODB/Connection.py", line 857, in setstate
    raise ConnectionStateError(msg)
ConnectionStateError: Shouldn't load state for 0x6c90 when the connection is closed

Try to import module before it is added to environment this way if user tries to import non existent module Exception is immediately raised and doesn't block next Jupyter cell execution.

Adds the support of filtering with Ledgers for the generation of the French Fiscal Report (aka FEC).

/reviewed-on nexedi/erp5!195

If user using Jupyter with ERP5 kernel is simply passing a comment inside a cell a server side error is raised thus this commit properly fixes it.
Clean up & style.