Fix review request field sizing issues and hide unused fields.

Review request fields were never shown very well. They had a hacky setup
that caused them to jump when the content changed, such as more text or
an inline editor being shown. This was ugly and I just won't stand it
anymore.

Now instead of a 4 column approach (which was really the core issue, as
it meant that the table was reevaluating its layout based on any new
content all the time and causing things to jump), we have two tables
floated next to each other, each taking up 50% of the space.

These tables will no longer intrude on each others' space, preventing
things from jumping around.

A nice side-benefit is that when resized really small (such as on mobile
devices), the tables will themselves wrap, moving to a single column.

Along with this, I've changed the template to not show the Change Number
field unless one is present, and not show Repository unless it's a
repository-backed review request. This simplifies things in certain
cases.
Fix rendering of text file thumbnails for unopened files.

Text file thumbnails, when accessed via the API, didn't have access to
an opened file. This was causing an error when attempting to read the
file data. The solution is just to open the file before doing any
reading from it.

Fixes bug #2805
Update the default branch for review requests for the release-1.7.x branch.
Merge branch 'release-1.7.x'
Dynamically generate the webapi resource tree docs.

The webapi resource tree docs were hand-generated, and out of date.
This adds a new ReST directive to spit out a resource tree based on
what's in the webapi resources list.
Stop including flup.

flup is needed for fastcgi, but their site has been down for a while
now, and we recommend wsgi, so stop bundling it with Review Board.
Add resource docs for review group user lists.
Document the missing webapi errors.
Fix a typo in the Group Already Exists API error.

A space was missing between "already" and "exists."
Fix the examples for resource payloads in the webapi docs.

We were showing examples for every allowed mimetype for a resource, but
this meant that we ended up showing both the generic (application/json)
and specific (application/vnd.reviewboard.org.<resource>+json)
mimetypes. To make it worse, we didn't apply proper formatting to the
latter.

We now filter out the generic mimetypes that we know we'll have
specifics for, and make sure to be smart about when to apply formatting
to mimetypes.
Merge branch 'release-1.6.x' into release-1.7.x
Add the new resources to the index.
Merge branch 'release-1.6.x' into release-1.7.x
Merge branch 'release-1.7.x'
Switch over to file attachments entirely in place of screenshot uploading.

This removes the ability to upload screenshots, and instead moves to
using file attachments for everything.

Dragging-and-dropping a file over the review request will just have a
big "Drop to Upload" link, instead of "Drop Screenshot" and
"Drop File Attachment."

The "Upload Screenshot" link on a review request is gone.

The entry for a non-repository review request now says
"(None - File attachments only)" instead of "(None - Graphics only)".
Show the thumbnail for a file attachment after uploading to a review request.

When uploading a file attachment onto a review request, we weren't
showing the thumbnail until we reloaded the page. That data was
available to us as part of the API, we just weren't using it. Now we set
the thumbnail when building the file attachment display.
Immediately display the reply draft banner after adding a comment.

The reply draft banner wasn't first showing up until after scrolling or
resizing the window. This was due to the banner not having a container
until later in the call stack. To work around this, we just need to
defer the initial call to update the position until the call stack
unwinds, since we'll then have a container and can make the proper
computations.
Set a tracking branch for commits on origin/release-1.7.x.
HostingServices can check if SSH keys are associated

Automatic SSH key association should only be performed if the key has not
already been associated. HostingServices that support SSH key association now
have the capability to report if a given key has been associated with a given
repository. Currently, only the GitHub HostingService supports SSH key
association.

Added unit test for code that checks if a key has been associated. Made slight
adjustment to key association test to ensure tests pass (given that a helper
method for SSH key association API calls was added). Both unit tests pass.

Tested manually with an existing GitHub repository by:

1) Adding RB server's (dev server's) SSH key to list of repository deploy keys.
   Check confirmed key was associated.
2) Adding SSH key to list of user keys. Check confirmed key was associated.
3) Ensuring key NOT associated with repository. Check confirmed key NOT
   associated.
4) Ensured associate_ssh_key still works as normal for GitHub.

Reviewed at http://reviews.reviewboard.org/r/3478/
Fix a regression with updating extra comment data.

The newly introduced _import_extra_data wasn't handling deletion of data
very well, and this broke unit tests.