android: parameterize GUI framework

contrib/android/Makefile

@@ -28,7 +28,6 @@ theming:
 	#$(PYTHON) -m kivy.atlas ../../electrum/gui/kivy/theming/atlas/light 1024 ../../electrum/gui/kivy/theming/light/*.png
 prepare:
 	# running pre build setup
-	@cp buildozer_qml.spec ../../buildozer.spec
 	# copy electrum to main.py
 	@cp buildozer_$(ELEC_APK_GUI).spec ../../buildozer.spec
 	@cp ../../run_electrum ../../main.py

contrib/android/make_apk

@@ -8,6 +8,9 @@ PROJECT_ROOT="$CONTRIB"/..
 PACKAGES="$PROJECT_ROOT"/packages/
 LOCALE="$PROJECT_ROOT"/electrum/locale/
 
+# qml or kivy
+export ELEC_APK_GUI=qml
+
 . "$CONTRIB"/build_tools_util.sh