Instead of having a complex auto-increment category manager that had
additional caching, just hardcode the (currently 6) ids for each
category, which allows us to simplify a lot of code.
If Parsoid sends a lint error in a category that we don't know about, it
is silently dropped.
Bug: T151287
Change-Id: Ice6edf1b7985390aa0c1c410d357bc565bb69108
linter_cat is now an int ID that points to a row in the new
lint_categories table.
The mapping between category names and ids is all handled in PHP, and
cached in APC.
Note that you will need to drop the `linter` table manually and re-run
update.php for this to take effect.
Change-Id: I369d9b4d8d08289b4a20d1cd29a2e327bad28ef8
