Remove vector clocks

Vector clocks are now replaced with a (value, timestamp, uuid)
triple. When two triples are joined, the one with the higher
timestamp will be chosen. The UUID is randomly generated for each
triple; its only purpose is to break ties.

This commit also removes a bunch of logic for supporting /ajax,
because it's being replaced by the ReQL admin API anyway, and
removing it was less effort than updating it.
Remove junk file; fix bug; fix style issues.
Make versioned_t::make_initial into a constructor. Add a bunch of comments.
Remove vector clock conflict test; it makes no sense now that we don't have vector clocks.
Mark versioned_t constructor explicit.
Remove unused parameters in administrative_http_server_manager_t constructor.
Merge branch 'tim_no_vector_clocks' into reql_admin