Add six

This is a requirement of pyelasticsearch 0.5 which added support for
Python 3.
Update pyelasticsearch to 0.5

This picks up the settings API stuff which we'll use at some point.
[bug 838638] Add SearchMappingTypes and rework indexing (1/2)

This adds a parallel universe of indexing which the es_reindex_cmd
and admin code will use to create the new index with the new
SearchMappingType code.

It also adds a bunch of TODO lines for things that need to be fixed
in the subsequent commit.

Comments out one test that gets whiny with the parallel indexing
worlds.
[bug 838638] Update views for new mapping types (2/2)

This updates everything to use the new mapping types and ditching the
old unified doctype.
Remove invalid tests.

These must've come along when we forked forums into kbforums.
They don't make sense here, we don't have these permissions in
the kbforums.
[bug 784351] Add ratelimiting to kbforum posting.
Use DocumentMappingType on search troubleshooting page.
[bug 870336] Use mapping type, not model.
Add index time in auto_lock_old_questions
[bug 869462] HTML emails for questions
[bug 869463] HTML emails for users app
Use email_utils.make_mail to preflight emails`
Fix typo
Fix circular import and remove no longer needed Markup()
[bug 870147] Summarize question page tweaks
[bug 651230] Warning for non-supported FF versions