Removing unused method: AccessToke.Create
Fixing 'Key not found'
RavenDB-1787 OAuth support in RavenFS client. Authorization is configured by new section in ApiKeyDefinition document - FileSystems
RavenDB-1787 Synchronization between servers with OAuth is working (it needs more tests and some refactoring)
RavenDB-1787 Synchronization to server with enabled OAuth works for content update, metadata update, file rename and file delete operations.

* refactoring synchronization task and related classes to use SynchronizationClient
* SynchronizationClient shouldn't use ExecuteWithReplication because we want to talk just to related, destination server
* extracting inner requests execution by SynchronizationWorkItems to SynchronizationClient
Set proper api key according to synchronization destination
Since we have RavenFS tenants urls should always contain tenant name
Better implementation of EnsureFileSystemExists
Put file system in appropriate directory