Bug 824037: Initial infrastructure to bring back page deletion.

This replaces deletion with more of a "trash can" effect; a deleted
Document remains in the database, but is excluded from queries. A
separate "purge" method can actually permanently remove the Document.

Additionally, the deletion mechanism differentiates between actual
Documents, and redirects; redirects can always just be deleted in one
go, rather than lingering in the database.

Additional work still needed:

1. UI for trusted users to be able to "purge".

2. Code and UI-level support, when someone attempts to create a new
   Document with the same locale/slug as a deleted one, for informing
   the user what's going on and giving them the option to start from
   the last revision of the deleted Document or just start fresh.
bug 917748: Preserve manually-supplied ID on <section>s
fix bug 917488 - Update global redesign - progress
fix bug 877239 - Reverse order of 'next' and 'prev' in redesign
Merge pull request #1388 from lmorchard/917748-manual-section-id-fix

bug 917748: Preserve manually-supplied ID on <section>s
fix bug 917784 - Better line height in PRE elements
Merge pull request #1391 from darkwing/redesign-search-pagination-877239

fix bug 877239 - Reverse order of 'next' and 'prev' in redesign
Merge pull request #1392 from darkwing/line-numbers-917784

fix bug 917784 - Better line height in PRE elements
Merge pull request #1389 from darkwing/redesign-nav-917488

fix bug 917488 - Update global redesign - progress
Merge pull request #1293 from ubernostrum/page-deletion-824037

Bug 824037: Initial infrastructure to bring back page deletion.
Fixed the wiki model migrations.

- remove the duplicate addition of the Document.deleted field
- don't use a specific datetime for a few datetime fields (triggered by a bug in an old south)
- make sure the db_index parameter is set correctly
Merge pull request #1394 from jezdez/fix-wiki-migrations

Fixed the wiki model migrations.