feat!: improve error handling

[Laupetin]

• Previously error handling was barely implemented, no timeouts were specified.
  To combat this, the client now tries to constantly reconnect to the server if disconnected with gradually increasing backoffs.
• When backing off, authentication and state are now cleared as well.
• JavaDoc was added for a lot of methods that are exposed to the outside.
• Non recoverable errors are now wrapped in a MatrixCommunicationException.
• Non-critical errors are exposed as return values in their appropriate functions.
• The MatrixClient implementation is now internal, only an interface is exposed.