Fix a bad assumption in the new binary file download logic.

The new logic for showing download icons for binary files made the bad
assumption that there was a FileAttachment we could query. We'd fail if
not.

We now check if the attachment is truthy before attempting to get the
URL.
Add API fields for review request counters and add new query args.

The Review Request resource now provides fields for `ship_it_count`,
`issue_open_count`, `issue_dropped_count`, and `issue_resolved_count`.

Callers can filter these for exact matches by passing, say,
`?ship-it-count=<value>`. It can also filter through ranges by
appending `_lt`, `_lte`, `_gt`, or `_gte` on the query parameter.
The results will be filtered accordingly.
Add the server info and capabilities to the root resource.

Nearly every client request RBTools makes needs to fetch both the root
resource and the server info resource.

The server info is pretty useful for most clients, especially the
capabilities and version information, so putting it in a separate
resource basically just results in one extra request.

Since the data is cheap and useful, it's now located in the root
resource. The server info resource still exists and mirrors the same
data, but clients can now check the root resource first.
Reduce the fadeout delay of the Loading indicator.

The Loading indicator was given a 1 second delay in order to not just
flash on and off on some requests, so that users can see that their
request had indeed started and finished.

1 second is a while, so this drops it down to 250ms. Testing with my
local server, it was on the screen just long enough to show the request
started and completed, but short enough to feel like the request
finished quickly.

This should give the perception of a large speed boost.
Include the LocalSite's public flag in the admin UI listing.

This is a useful enough flag to list, so show it in the list of local
sites in the admin UI.
Fix bugs in "Depends On" field.

The depends on field had some lingering problems:
* Change descriptions weren't rendered properly, just saying "added" and
  "removed" without actually including the IDs that were changed.
* Creating a new draft wouldn't copy over the old values, which meant that
  making unrelated changes would clear out the field.

Testing done:
* Added and removed a bunch of dependencies.
* Ran unit tests

Fixes bugs 3073, 3139

Reviewed at https://reviews.reviewboard.org/r/5294/