lib/android: Intro API wrapping android SharedPreferences

Signed-off-by: Frédéric Vachon <fredvac@gmail.com>
lib/android: Added shared_preferences import into mnit_android.nit

Signed-off-by: Frédéric Vachon <fredvac@gmail.com>
lib/android: Added tests to mnit_simple

Signed-off-by: Frédéric Vachon <fredvac@gmail.com>