Merge error: SignInActivity overflow menu added
remove unused ids
reenabled the newest crashlytics gradle plugin due to bugfix
signing request instead the url to enable caching
enabled landcape view for some activities, specified actionbar splitting for activities
change of type form message folder messages
use message folders array position for the request...

...to conform the APIs strange behavior :expressionless:
Merge branch 'message-folders-fix'
moved volleys request queue to Application.class
all request using Application.class request queue, organized imports
removed old singleton class
Merge branch 'volley-to-application'
added studip mobile red for later use
file icons for supported file types
mapping of MIME type to drawable
usage of new MIME type to drawable mapping
Merge branch 'new_document_icons'
changed gerneric files icon to a more adequate one
strings for showing < 4.0 users at in the downloads section a not supported warning dialog
check if the api level is below 14 and show a not supported warning