remove unneeded global variables

lists of users in the main activity is not accessed from anywhere
else than displayDialogEnableDisable so they should be local variables
instead of global.
fix type in help strings
remove unused message handler

scheduled backups do not display any progressdialogs, only
notifications, so HandleMessages is not needed.
remove unneeded global variables

also temporary fix for race condition when returning from
batchactivity
use adapter.getItem in context menu

otherwise the appinfo is pulled from the original list which
will cause problems if the shown list has been filtered or sorted.
message handler as static class

handle messages with a static handler class to prevent memory
leaks.
send the message data as a bundle to make it more clear what
is used for which purposes and make it more controlled.
Merge branch 'handlemessages'
share option in context menu

share dialog implemented as an alertdialog but should ideally
be a multichoice list or a custom dialog to support more options
than the current three.
currently, sharing is limited to sharing apk and/or data folder,
but sharing the logfile and sharing multiple apps could be
implmented too.