add icons, and interface lines

 Changes to be committed:
	new file:   res/drawable-hdpi/ic_settings_performance.png
	modified:   res/drawable-hdpi/ic_settings_themes.png
	new file:   res/drawable-mdpi/ic_settings_performance.png
	modified:   res/drawable-mdpi/ic_settings_themes.png
	new file:   res/drawable-xhdpi/ic_settings_performance.png
	modified:   res/drawable-xhdpi/ic_settings_themes.png
	modified:   res/values/raumzero_strings.xml
	modified:   res/xml/settings_headers.xml