redis-backed "mentions" timeline as redundant (given notifications)

affected, replaced onClick handler with onMouseUp/Down to detect text
selection not trigger onClick handler then

application website validation, don't link to app website if website isn't set,
also comment out animated boost icon from #464 until it's consistent with non-animated version

A couple of places were using "reblog" rather than "boost" - this updates them to match the web UI

Reflect "requested" relationship in API and UI
Reflect inability of private posts to be reblogged in the UI
Disable Webfinger for locked accounts

Filters out hidden stream entries from Atom feed
Blocks now generate hidden stream entries, can be used to federate blocks
Private statuses cannot be reblogged (generates generic 422 error for now)
POST /api/v1/statuses now takes visibility=(public|unlisted|private) param instead of unlisted boolean
Statuses JSON now contains visibility=(public|unlisted|private) field

removing web app capability from non-webapp pages

Do not autoplay videos, display play button instead. Use expiring links when using S3. Do not keep originals
for avatars/headers, resize avatars down to 120x120 instead of 300x300. Set cache headers on S3 stuff, also
make it private (aka only accessible via expiring links to prevent hotlinking)

Fix #233, fix #268