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

Unhide completions, strengthen shadows a bit, force the 0.1 shade to always span the full height, make usercard use correct borders.

Move custom theming from settings to style-switcher, remove usage of custom .css files, use styles.json instead.

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

Also fetch user if not in the state already.

Give tall notifications either a scrollbar (mentions), or just cap them and use a cool hider (fav/rt).

Move previews from conversation to status, put the reply preview arrow back on timeline statuses, add a spinner when the preview is still loading.

Add an option to automatically show new posts when scrolled to the top, also add fade-in animation for posts.