Add loading indicator for notifications, make timelines indicate bottoming out when no more statuses

belongs. Changed display of profile to single panel with tabs.

generation for alerts, updated getTextColor to also have fallback to black/white
if resulting contrast isn't passable (only when inverting lightness!), updated
UI to use tabs.

from settings screen.

attempt to recognize when holes in timeline for various reasons, clear timeline and fetch older when showing new to get rid of holes

Update theme editor to have 4 colors, rewrite the color setter, change a LOT of base16 assignments for better consistency.

Round the edge of the user profile user card, make sure 'follows you' stays in the right, fix avatar class conflict.