also gcs credentials are now encrypted, both on disk and inside the
provider.
Data provider is automatically migrated and load data will accept
old format too but you should upgrade to the new format to avoid future
issues
This way you can force the user to login again and so to use the updated
configuration.
A deleted user will be automatically disconnected.
Fixes#163
Improved some docs too.
The common package defines the interfaces that a protocol must implement
and contain code that can be shared among supported protocols.
This way should be easier to support new protocols
