feat(android): custom gallery folder names

[m1ga]

Currently if you use saveToPhotoGallery the images will be added into the normal Pictures folder on Android. You can't create any subfolders like WhatsApp is doing. This PR will add a new property galleryFolder where you can add a string that will be used as a subfolder:

var win = Ti.UI.createWindow()
win.open();
win.addEventListener("click", function() {
	Ti.Media.requestCameraPermissions(function(e) {
		if (e.success) {
			Ti.Media.showCamera({
				saveToPhotoGallery: true,
				galleryFolder: "myCustomFolder",
				success: function(e) {}
			})
		}
	});
})

Todo:

• iOS ?
• documentation