BE: Create channel - asymmetric encryption

[dominic22]

• Add channel type PrivatePlus to is-shared-modules
  • update of is-shared-modules
• When creating such a channel it needs to be checked if the author has a encryption key in his identity document
  • add public encryption key to the subscription as field asymKey
  • Use this asymmetric key to encrypt the state of the author
  • Use this asymmetric key to encrypt all the channel data the author is reading/writing
• add tests

[dominic22]

story splitted