layout_html_overflow-y_auto

Changing behaviour of clipping top/bottom edges of the html block to
auto, thus only adding Y axis scroll bar when needed.
Add fixture helper
Move HummingbirdListImport to ListImport::Hummingbird
Port the MyAnimeList import to the new ListImport system
Delete substories in a background thread.
Dedicated queue for story fanout.
Add redis connection pool.
Merge pull request #256 from infrequent/master

Layout html overflow-y auto, rebased
Don't fanout followed stories.
Convert all redis usage to use the connection pool.
Changed manga note type to allow >255 strings
Chat online users implementation.
Fix message_bus delivery delay.
Bottom scroll observer.
Chat route deactivate bugfix.
Flexbox-ify chat panel
Fix scroll to bottom, height 100%
Fix left column.
Try to fix formatted messages.
Show number of online users.