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/