theme selector - use gengrid instead of list

this makes the theme selector look much nicer. it's a step in the
right direction, but not 100% there. did this more as an example for
people filling in wallpaper and color selector (colors will need to
have a scheme/theme and preview too and then a way to edit a custom
theme/scheme).
cleanup options code
add dummy option about key bindings
have a list with the keybindings

This is ugly, makes evas complain… but it's better than nothing and users
might discover the bindings about the "tab" switcher…
And we're in feature-freeze.