Context

We currently count incoming hotline messages as broadcast messages, which is bad because it skews our "broadcastOut" numbers a lot (by multiplying every hotline message by number of subscribers instead of number of admins, so it looks like a lot more broadcast messages went out than actually did)
Plus it would be nice to have visibility into how many incoming hotline messages v. outgoing broadcast messages are happening overall to develop a better intuition for how people use the app

Changes

create new messageCount fields for hotlineIn / hotlineOut
increment them appropriately after forwarding a hotline message
modify the response to boost list-channels to:
- sort by number of subscribers, descending (instead of by broadcastOut, which is a dumb metric anyway!)
- show broadcastIn, hotlineIn, and commandIn counts for each channel (don't show broadcastOut)
zero out all messageCounts for all channels and start fresh with clean (no-bug) counts

add hotline fields to messageCount table/model
extract all counting logic to repositories.messageCount (eliminate helpers from dispatcher.messenger)
add respositories.messageCount.countHotline and call it in messenger.relayHotlineMessage
- lleanup tail end of relayHotlineMessage to avoid double counting an incoming hotline message as a command
modify repository.channel.findAllDeep to not sort by anything
modify registrar.channel._formatForList to show broadCastIn and hotlineIn and sort by subscribers
add a migration to set all messageCounts to zero and start fresh with clean data