Material design: List: Specify elevation.

Though it's not clear how this should really be used,
and I doubt it will have a visible appearance on a dark theme.
Remove unnecessary imports.
Action icons: Update the help icon to the latest from the Android Asset Studio.

This apparently the correct one to use with Material Design.

ic_action_help was generated from this:
http://romannurik.github.io/AndroidAssetStudio/icons-actionbar.html#source.type=clipart&source.space.trim=1&source.space.pad=0&source.clipart=res%2Fclipart%2Ficons%2Faction_help.svg&name=ic_action_action_help&theme=light&color=33b5e5%2C60

I can't tell if the other icons need to be updated too.