To be able to set a theme from the firmware itself, we need a couple of helper
methods. First, we need to be able to update the palette without using Focus,
and we also need to be able to update a single LED without committing it. On top
of that, we'll likely want to know if the theme is initialized.
To this end, we introduce `updatePaletteColor()`, which updates an entry in the
palette, but does not commit it, and `isThemeUninitialized()` which does as the
name suggests: it checks if the palette and the theme slices are all uninitialized.
We also change `updateColorIndexAtPosition()` to not commit. The single user of
it was FingerPainter, and we update that to do an explicit commit after.
Signed-off-by: Gergely Nagy <algernon@keyboard.io>