purge unused code: PassphraseActivity
create static GnuPG class to handle the global GnuPGContext instance
use a Log TAG for each activity instead of a global GPGApplication.TAG

It seems that GPGApplication is not really needed, so this is a step
towards eliminating it.
rename InstallTask to InstallAndSetupTask since it handles the setup too
move Context out of GPGApplication to where its needed

This is another step into refactorting GPGApplication away.  The
android.app.Application class is meant more for handling global changes of
app state rather than for global variables.
clean up PinEntryActivity's layout
move version stuff to GnuPrivacyGuard and eliminate GPGApplication

After reading about the android.app.Application class, its not really
intended to be a global state class.  It is meant to handle global state
changes, and has a specific API.  GnuPrivacyGuard.java is currently two
things combined: 1) the global app repo of variables, and 2) the test log
view.  The test log view should be split out of GnuPrivacyGuard.java.
when starting dirmngr/pinentry onBoot, also start gpg-agent