WIP: Model sync

starting with an interface for syncing changes between objects stored in a local or remote data store. The interface for now includes:

## ObjectHandle

### read
- `#get`
- `#subscribe`

### write
- `#set`
- `#commit` (set ensuring no overwrites)

##  Local Store
- currently synchronous object store
- outlines an interface required by any store

Thinks I'm working on:
- remote store
- (sub)handle access
- reading tree changes
- synchronization for collections