Several changes in RavenFS studio and FilesStore

- Adding support for metadata changes in AsyncFileSession
- Implemented support for MetadataChangedListener in FIleStore (RavenDB-2473)
- Added several tests for the File Session and Store
- Fixed some minor issues in the studio
- Fixed RavenDB-2549
- Make breadcrum consistent for all the views of RavenFS Studio
- Fixed RavenDB-2548
- Fixed several issues in the Search and Configuration views in the Studio
- Fixed issues in the Files view in the Studio