When android.permissions list is left blank, it contains a null string [""]
Filter this out when checking permission validity, and when building --permission command line args

Also fix two typos in the error message for an unknown permission
Revert "When android.permissions list is left blank, it contains a null string [""]"

This reverts commit aa0a7f8195716a4487dd1ab8c863be7930e45c06.
_get_config_list() was incorrectly returning [""] instead of [] for blank config lists
presplash.filename and icon.filename only worked if source.dir was .
For any other value of source.dir presplash and icon were broken.
android: if multiples devices are plugged, deploy and run on all of them. except if a ANDROID_SERIAL env is set.
add support for orientation and fullscreen (working on android only right now.)
Merge branch 'master' of https://github.com/kivy/buildozer

Conflicts:
	buildozer/__init__.py
	buildozer/targets/android.py