Support nested partitions and partitions directly targeting services (#122)

* Do the nested partition thing

* Tidy up touched code

* Add nested partition test project, not fully functional

* Clean up variable names, move path_metadata mutation strictly into snapshot_reconciler

* Remove path_metadata, snapshotting is now pure

* Factor out snapshot metadata storage to fix a missing case

* Pull instance_name out of per_path_metadata, closer to what we need

* Refactor to make metadata make more sense, part one

* All appears to be well

* Cull 'metadata_per_path' in favor of 'instances_per_path'

* Remove SnapshotContext

* InstanceMetadata -> PublicInstanceMetadata in web module

* Build in snapshot testing system for testing... snapshots?

* Remove pretty_assertions to see if it fixes a snapshot comparison bug

* Reintroduce pretty assertions, it's not the cause of inequality

* Fix snapshot tests with custom relative path serializer

server/src/fs_watcher.rs

@@ -44,13 +44,14 @@ impl FsWatcher {
             let imfs = imfs.lock().unwrap();
 
             for root_path in imfs.get_roots() {
+                trace!("Watching path {}", root_path.display());
                 watcher.watch(root_path, RecursiveMode::Recursive)
                     .expect("Could not watch directory");
             }
         }
 
         {
-           let imfs = Arc::clone(&imfs);
+            let imfs = Arc::clone(&imfs);
             let rbx_session = rbx_session.as_ref().map(Arc::clone);
 
             thread::spawn(move || {