subclass Application to cleanly handle installing assets (fixes #1358)

It adds InstallActivity to show the ProgressDialog when installing.

This replaces the code that was originally in GnuPrivacyGuard.java and was
then moved to MainActivity.  Its currently an AsyncTask, but should be
replaced by a unkillable Service.
merge all methods starting the services into static ones in GpgApplication (issue #1250)
move version and package name constants to GpgApplication (issue #1250)
prevent NullPointerExceptions while saving state in MainActivity
REBASE into     move version and package name constants to GpgApplication (issue #1250)
if install is needed, insert it before MainActivity shows its content

MainActivity is currently gets LAUNCHER intents, so its the first to start,
except for the BroadcastReceiver and perhaps the file associations. The
installation of the gnupg guts needs to happen before anything else,
whether this is a new install or an upgrade. So before MainActivity checks
whether to run the wizard or sets up its layout, it checks whether install
needs to be run, then runs it.
move pidof() and kill9() from NativeHelper to Posix

pidof() and kill9() emulate Posix shell commands, so this seems like a
natural home for them.