Use promises to coordinate data loading

This will make it easier to handle failures among other things.
Refactor loading sequence to leverage promises

This was pretty haphazard, and still could use some further refinement.
We now rely on the promises exposed by the loading to coordinate
startup.

In particular responses could come back ahead of templateDidLoad which
led to problems in changing feed buttons without knowing which feed
buttons existed.
Improve concatenation of params

Not as bulletproof as it should be but this was quicker than
figuring out which url library to use right now to properly resolve
the params.

Otherwise we had a situation where params might be added with an &
intend of a leading ?
Add offline support

This is a local copy of the feeds and images as of today, for
offline support. We will need to replace this with some cached
localStorage system to avoid storing the images ourselves.
Merge branch 'master-orig'

* master-orig:
  Add offline support
  Improve concatenation of params
  Refactor loading sequence to leverage promises
  Use promises to coordinate data loading