[#6545] re-order app_config_id,label index so it can be shared

..shared with the main app_config_id index.  It was added in 1fc1d377
for faster ticket label lookup, but the order doesn't matter, so
better to share the first part of the index.
[#6545] remove old indexes and code; add 'timestamp' to discussion_id,status index

* Message's index on timestamp was added in 76e8541c for stats on ticket comments,
  our new index is a better fit
* Message's slug & parent_id indexes were added in ebb201de for now-unused
  replies() and descendants() methods
[#6545] [#5907] use status in last_post()

* we only want to show approved posts
* it uses the (discussion_id, status, timestamp) index
[#6545] Add graph of forum posts
[#6545] remove SF-specific ticket graph (was deteriorating anyway)
[#6545] add CSS for daterange picker, graph
[#6545] tweak graph point size
[#6545] ignore query string when checking for active sidebar item
[#6545] bump ming version for query.aggregate
[#6545] tests
[#6545] add forum selector
[#6545] Fix typo

Signed-off-by: Tim Van Steenburgh <tvansteenburgh@gmail.com>
[#6545] Remove hint() - no longer needed

Signed-off-by: Tim Van Steenburgh <tvansteenburgh@gmail.com>
[#6545] 'All' forums is empty string, not None

Signed-off-by: Tim Van Steenburgh <tvansteenburgh@gmail.com>