Use a dropdown instead of arrows for switching between comparisons

[wooferzfg]

We have 9+ different comparisons, and having to use arrows to switch between them is pretty unintuitive. We should definitely still keep the hotkeys for switching between comparisons, but the comparison selection in the sidebar should be a dropdown menu.

[CryZe]

I'll mark this as iOS because on iOS the arrows aren't even properly fitting into the sidebar and flow into the new line. So the current implementation is basically "broken" for iOS atm (though this should be an easy fix via grid or flexbox, but idk if we want to do that when we want to replace the whole thing anyway).

[wooferzfg]

For this, we'll need to:

• Expose Run.comparisons in the C API so that we have a way to get a list of all the comparisons.
• Expose Timer.set_current_comparison in the C API so we have a way to update the current comparison based on a string.
• Update LiveSplit One to show a dropdown with all the comparisons instead of arrows.

[wooferzfg]

It would also be useful to show a dropdown for choosing a comparison override in the settings.

[CryZe]

I believe I want lsc to just generically define comboboxes (i.e. it just returns a list of options) for settings, so while it would technically be useful there, lsc can just fill the list by itself, in this case.