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 the URL to the new android mobile client
Add gem 'better_errors'
Update bigbluebutton-api-ruby and bigbluebutton_rails
First changes for the new logic when joining via mobile

There will be a single button to join a conference. If the user is in a mobile
device, the mobile client will be automatically triggered. The old modal window
to join via mobile was removed.

Made a new "mobile" layout, currently only used in the page shown to join a
conference from a mobile client, but that can be used for more in the future.
Show right count on manager users
Use newer version of forgery to avoid timezone bug
Small improvement checking whether a space logo is being cropped

refs #1049
Fix wrong test for User

Tests were passing, but the setup before the test was wrong.
Fix recursive redirect to /user/login

After 1358a1f6a87e7

refs #1231
Use select2 for timezones refs #275
Use select2 for timezones in sites/edit

Complements f8a672a

refs #275
Fix permissions for join requests

Inviting people to join a space was giving permissions errors.

refs #1252
Update mweb_events

refs #1226
Fix missing partial destroy_space in manage/spaces
Add missing shib_env_variables to sites/edit and sites/show

Also improved some strings related to shibboleth and the account association
view.
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