The Activity context may not be available, so it's safer and simpler
to use the always available app context.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Android apps may want to run Go code independent of the Gio Android Activity.
Expose a Gio.init Java method public for early loading and initialization of
the Go library.
Signed-off-by: Elias Naur <mail@eliasnaur.com>