A user can delete himself

[mreider]

Later we can try to delete all
Messages and things from the browser too.

[falconandy]

Added new API:

POST http://localhost:12002/rpc.UserService/DeleteMe
Authorization: Bearer AUTH-TOKEN
Content-Type: application/json

{}

POST http://localhost:12001/rpc.UserService/DeleteMe
Content-Type: application/json

{}