The Checklist Extension

The Checklist extension allows users to create a checklist when they are
reviewing a request. This is useful for cases when there are many things to
check for, and the reviewer may want to keep track of them.

The app allows:
- Auto creation of a new checklist upon viewing a new review request
- Adding new items to the checklist
- Editing existing items
- Deleting items
- Checking off items
- Undoing checked items
- Minimizing checklist
- Maximizing checklist
- Deleting checklist

The extension is a seperate Django app, and does not modify any of the
Reviewboard code. It can be enabled through the Admin page, in the Extension
tab.

Testing Done:
Manual testing on Chrome and Firefox:
- Created checklists by viewing new review requests
- Added items on the checklist
- Deleted items on checklist
- Modified items on checklist
- Checking off items
- Undoing checked items
- Tested on different file attachments but same requests
- Tested on different review requests
- Tested on different users

This commit does not include the images which were used in the original change,
because they weren't posted (and I don't see a fork that includes them). The
missing files are:
- checklist/checklist/static/images/cross.png
- checklist/checklist/static/images/exit.png
- checklist/checklist/static/images/max.png
- checklist/checklist/static/images/min.png
- checklist/checklist/static/images/plus.png

I'm also not sure why there's both a "style.less" and "index.css" file. It
looks like one is derived from the other, but it's the .css file which is
bundled in the extension. We'll have to investigate this.

Reviewed at https://reviews.reviewboard.org/r/5007/
Add missing __init__.py file and update apply_to pages.

Added missing file that doesn't allow Checklist Extension to be accepted by
Python, also, updated apply_to to use the correct urls.

Reviewed at https://reviews.reviewboard.org/r/5890/
Modified checklist extension to use style.less

Modified the extension so that it uses style.less instead of css file.

Testing Done:
Manual testing on Chrome and Firefox:
* Added items to the list
* Checked items off the checklist
* Unchecked items on the checklist
* Deleted items from the checklsit
* Minimize the checklist
* Maximize the checklist
* Delete the whole checklist
* Start a new checklist by refreshing the page

Reviewed at https://reviews.reviewboard.org/r/5932/
Changed Checklist template format

The template has been recreated using unordered lists, rather than tables.
Also, the layout of the extension has be alternated; the input text field was
moved to the buttom of the extenson. All icons have been replaced with text
links, which fit better with RB style.

Testing Done:
Run RB with checklist extenion enabled on Chrome and Firefox browser, they both
have consistent look.

Reviewed at https://reviews.reviewboard.org/r/5933/
Changed style of Checklist extension to fit RB colour scheme.

This change makes several alterations to the style for the checklist. The
checklist is now drawn in a light blue, matching the colors used in the rest of
Review Board. This also eliminates the icons in favor of text links.

Testing done:
Ran with the checklist extension enabled and saw the new styles.

Reviewed at https://reviews.reviewboard.org/r/5939/
Make a couple small changes to the checklist styles.

This fixes the bottom border and size of the input box in the checklist.
Trivial changes.
Merge branch 'dev/checklist-extension'

Now that we have a clear distinction for what is "released" and what is not
(the package store), there's no good reason to have this in a separate branch.
Merging to master.