Cached invalid repository connection

[kavics]

There are two scenarios.

The good case: The client starts and gets a repository that works correctly. After any network error, the reconnection can be successful and the work can continue.

The worst case: The client starts and gets a repository that does not work correctly because of any reason. Work is impossible, even after a successful connection. There is only one option: the client must be restarted.

The reason: The IRepositoryCollection instance (from the services) caches repositories on first access. An unavailable repository has an empty access token forever, so the only accessible user for it can be the Visitor.

Possible solutions

• If the client can recognize this problem, it could solve it by invalidating the server cache (e.g. repositories. Reset();) and restart is not necessary.
• caching repositories for only a limited time in a real memory cache instead of a dictionary
• cache reset should target a single repository or maybe a server instance, not all of them

[tusmester]

We solved the shorter cache time in #119. We still need to add the Reset functionality because we do not want to wait for the cache to expire.