[Cloud.NET] fixes and improvements

- CHG: code improvements
- FIX: setting of file size in meta files
- ADD: own collection types for ClodFile and CloudDirectory objects in
SDK
- FIX: documentation
- FIX: typos
[Cloud.NET] exception handling

- CHG: "better" exceptions if file or directory does not exist
[Cloud.NET] first working alpha of file sync tool
[Cloud.NET] File syncer

- ADD:  file manager