check for error on apk restore before proceeding

check to avoid problems as descriped in issue #53
(https://github.com/jensstein/oandbackup/issues/53)
split batch operations into more methods

the doAction method of BatchActivity was very much too long
so backup and restore has been split to separate methods.
use newer method for showing message in batchactivity

also incrementing the counter is moved to the bottom where
it logically fits better.
toggle checkbox states when returning from batch

set all checkbox states to unchecked unconditionally when returning
to the main activity.
using newer setChecked instead of toggle to get rid of the extra check
to see if the item is checked.
move unnecessary global variable

no reason for listview to be a global variable.
also condensed a poorly written comment.
remove toggle method from appinfo

the toggle method has now been replaced in all instances with
setchecked().