Added the AsyncTaskResultWrapper
Reworked ImportKeysListFragment to handel exceptions, ImportKeyListLoader is temporarily disabled
Adapted the ImportKeysLoader to work with the new AsyncWrapper
Added documentation to the AsyncTaskResultWrapper
Added StackOverflow link to documentation
Added error strings for key import from keyserver
Added different notifys for different exceptions
Some clean up
Merge pull request #306 from danielhass/keyserver-conerror

Show error if keyserver is not reachable