add work-around for language persistency on older android versions

this fixes #48 which might be caused by an android bug.
locale changes unexpectedly when calling pm.getInstalledPackages(PackageManager.GET_ACTIVITIES) for the first time in the activity's lifecycle.
make utils methods static

also eliminates the need to have both context and activity as the activity
object is always a context
work-around for language change on older platforms

add check for language change on older android versions to
work around issue #47 (https://github.com/jensstein/oandbackup/issues/47)
this reloads the main activity on return from preferences