Take Updates, which are generated by Diff, and send them to the UI.

The C++ level and BlockC have no notion of "blocks" which may be shared between block views. The haskell State does have this notion, so it's this module's job to distribute an operation on a block to all of the C++ block views that are displaying that block.

So if this module has a bug, two views of one block could get out of sync and display different data. Hopefully that won't happen.

Implementation of merged tracks:

They need to be implemented in two places: 1. when a block is updated with changed merged tracks, and 2. when a track is updated they should be preserved. It's tricky because unlike normal track events, they are block level, not track level, so the same track in different blocks may be merged with different events. I don't actually see a lot of use-case for the same track in different blocks, but as long as I have it, it makes sense that it can have different merges in different blocks, since it's really a display-level effect.

This is a hassle because case 1 has to go hunt down the event info and case 2 has to go hunt down the per-block info, but such is life.