Initial modifications to change the rooms permissions in spaces.
Changed the web conference permissions in spaces

Formerly the permissions of the spaces were as follows:

 - All members of a space will be moderators in its web conference room;
 - All members of a space can start a web conference in the space;
 - All members of a space can stop a web conference in the space.

Now this is the new set of permissions:

 - Only administrators of a space and the person that started the web conference will be moderators;
 - All members of a space can start a web conference in the space;
 - Only administrators of a space and the person that started the web conference can stop the conference in the space.

Required the new version of the bigbluebutton_rails gem.

Refs #1148
Update mweb_events and several small improvements when showing events
Unify css for visibility of spaces and events

Different classes were being used. Now it's always "resource-visibility".
Update default space images, fix headless guy
Merge PR #19

Merge remote-tracking branch 'fbottin/Feature1148' into branch-v2
Improvements after PR #19

The most important was the removal of API calls to the webconf server from
Abilities. Now these calls are made by the controller and Abilities will only
check for information already fetched into the models.
Updated bigbluebutton_rails to have this change in effect.

The rest was a bit of refactoring in the changes from the PR.

refs #1148
Add an LDAP filter to restrict users that can log in

Added the column to Sites and implemented the basic use of this new filter.
Still to be properly tested against a real LDAP server.

refs #1257
Stub some BigbluebuttonRoom methods so that tests calling the API pass
Since we stubbed meeting running status, stub meeting creator to pass tests
New js component DateTimeInput to fix the invitation form

The invitation form now uses multiple inputs (<select>s) to select a time
and a datetimepicker to select a date (the same way is done for events in
mweb_events).
These inputs are grouped together in a new js class DateTimeInput.
Not finished yet, but the js part of the form is almost finished.
Finish separate date/time inputs in the webconf invitation form

Last overall changes in the controller, js and view to use separate inputs
for dates and times in the webconf invitation form.

Complements 1eb47cf09
Small improvement in a translation in pt-br
Add tests for ApplicationController#bigbluebutton_role

refs #1148
Small changes on LDAP log messages and strings

refs #1257
Merge branch '1257-add-ldap-filter' into branch-v2

refs #1257
Merge remote-tracking branch 'upstream/branch-v2' into branch-v2

Conflicts:
	db/schema.rb