This is a major change to the /#subscriptions page, converting it to
by a side-by-side list of streams and their settings in an overlay.
There are no new features added/removed, but it's a huge changeset,
because it replaces the old navigation logic and moves the stream
creation modal to appear in the right side of this overlay.
Filter behaves similarly to filter in left sidebar, see PR #684. Added
stream input field to the stream creation modal along with other settings,
for clarity.
Fixes#455, #563.
Brock Whittaker
Rafid Aslam
trueskawka
Vishnu Ks
Tim Abbott
Steve Howell