Remove header and footer handling and installation of .com hook.

Installing the hook will have to be done manually. The ultimate goal is to
stop copying posts over to the .com database, so this is a temporary measure.
Fix usage of $contrib->download - it may contain more than one download now.
Fix removal of sid in .com hook links.
Ensure that downloads are ordered from newest to oldest branch.
Fix display of ColorizeIt button in invalid instances.
Fix bug where "Allow repacking" option is not preserved when repacking.
Fix incorrect form action when repacking.
Fix incorrect check resulting in is_author_subscribed() method return invalid value.
Fix invalid class name.
Fix call to undefined method.
Add missing parameter.
Add initial support for multiple demos.
Add migration to update contrib_demo value to new multibranch format.
Display multiple demo URL's as a dropdown.
Remove root path "hack" when fetch user ranks.
Fix styles demo iframe source.
Fix instantiation of nonexistent auth class.
Add missing call to json_decode for result returned from style demo hook.