Define strings for failes uploads/downloads  with credentials errors
Use the new strings for upload and download fails when it is necessary
Merge branch 'develop' into more_concrete_error_messages_session_expires
New class ErrorMessageAdapter to choose proper error message to show to the user depending on the results of operations
Add specific message(s) for network error(s) in strings.xml
Use ErrorMessageAdapter to access the error string when an error in a finished foreground operation occurs
Merge pull request #505 from owncloud/more_concrete_error_messages_session_expires

More concrete error messages when session expires