Add some useful additions to the commenting and screenshot APIs.

The commenting APIs now have some additional data that can be used for
navigating to review UI URLs and seeing more info on what's being
commented on.

Diff comments can now be ordered by its fields. This is useful if you
want to get the list of all comments by file, in line number order.
Improve the style of the issue summary table.

This makes a few tweaks to the issue summary table. There's now more
padding in each row, making things less cramped. The double border has
also been removed, cleaning up the look. The "resolved" border is also a
lot less faint, blending in better with the other rows.

The description has been truncated at 20 words, which seems to be a
decent length. This keeps it from being a squashed mess.

The text in the cells are aligned to the top now, which helps with
wrapping. The description column now takes all the available space.

The Issue ID column has been removed. It wasn't really that useful and
didn't cleanly map (since the concept of an issue ID didn't exist
anywhere else).
Update the documentation for a modern Fedora/CentOS/Red Hat install.

This removes old references to the Fedora Extras repository from the
installation docs, and adds a couple sections on Fedora and other
Red Hat-based distros. These should help people get set up much quicker,
and avoid pitfalls based on old information.