Update migration docs and add command for migrating data.

Instead of checking out certain commits and running migrations, instead
we're going to just move to the latest, make a few manual DB changes,
and pull in the old data from a copy of the old database.

No unit tests for the migration are included since the command will 
really only be used twice or so, and manual testing is far easier for
this particular case.
Fix broken progress bar display on detail page.
Hook up size field on link detail page and fix text preview styles.
Ignore slave databases when migrating links.
Hook up dashboard stat display.
Need to format ranking number too, whoops!
bug 976229 - profile page template
Add migration to create profiles for users missing profiles.
Add verbose_name_plural for Category.
Remove profile link from about page.

Also refactors the header user code very slightly to be more concise.