remove need for context in filecreationhelper

context is removed and default paths for backupdir and
logfile are provided through static methods, so it isn't
necessary to store the filecreationhelper object in many
classes anymore.
check if objects still exist when returning to main activity

if user has 'don't keep activities' checked in developer options
appinfolist and sorter will be null when returning. check added so
they are not referenced before they are recreated.
write logfiles with a static method

remove the need for passing a context by doing the writing in
a static method and passing the dateformat boolean directly to
the it.
remove constant context object in shellcommands

pass the context object directly to the methods which need it
and instead pass a sharedpreferences object to the initializer.
don't store timestamp as string in logfiles

the timestamp string is calculated directly in appinfoadapter
instead. this makes it possible to remove the preferences boolean
from the other classes where it was passed unessecarily.