Menu UI tweaks

Change the learn/quiz/srs **Front** option menu to something more palatable than a slider. The slider feels unnatural for this purpose, but I'm still thinking about it. This page **Options** before starting a review feels a bit sparse. Play with the sizing and spacing of these items.

Additionally, add padding and filling around each button. This will probably be done during the UI overhaul, but it's still a good idea to put padding on some of the buttons at least to get a feel for the design and layout.

Start at the learn/quiz/srs Front option menu and the Options page shown before a review. Review the current slider, item sizing and spacing, and button padding, then confirm the intended replacement and layout direction before treating the UI overhaul as complete.

Written by the indexing model from the issue text.