Updates the `DaySeparator` component to have separately settable colours
for the text and the lines.
Updates existing overrides of the `DaySeparator` to use the new colour
setter.
Create new `ChatOverlayDrawableChannel` with adjusted spacing and new
`DaySeparator` colours.
Bad sign when you can't follow your own code.
All of the various state changing methods were flattened into one
because it was too hard to follow what was calling what and why.