Multi-tenancy cleanup, part 1: Remove 'seqn' and revert to row id everywhere.

External IDs may change for some objects -- anywhere where a row had been
removed (since the sequence number allocator would reuse IDs but an
autoincrement column may not).
Multi-tenancy cleanup, part 2: Remove kbsite name from URL routes.
Fix brewer image migration.
Handle epoch change.
Improve single drink detail page.
Update highcharts to 2.3.5
Clean up keg page.