Add the themes configuration entry point

Change-Id: I0eb669956d9e89bb92cd43487b14b4246454a400
Signed-off-by: Rohan Mathur <rohanmathur34@gmail.com>

Conflicts:
	res/values-cs/strings_custom.xml
	res/values/strings_custom.xml
	res/xml/settings_headers.xml

	new file:   res/drawable-hdpi/ic_settings_themes.png
	new file:   res/drawable-mdpi/ic_settings_themes.png
	new file:   res/drawable-xhdpi/ic_settings_themes.png
	new file:   res/values-cs/strings_custom.xml
	new file:   res/values/strings_custom.xml
	modified:   res/xml/settings_headers.xml