Manage the Client Profile

[claucece]

See where it will be published, if the serialization is ok, how it will be published and retrieved.

See issue otrv4/libotr-ng#108 of libotr-ng.

Tasks

• [x] Create and publish a client profile if there's none
• [x] Create a new client profile and publish after expiration
• [x] Update and publish the existing client profile if one of the values changes

[claucece]

On this we should include as well:

• [x] Check when reading a client profile that it is signed by the same private key that we have also read. Change it and publish new one if it changed.

[claucece]

cc. @giovaneliberato

[giovaneliberato]

I stopped working on this until #72 is done. This will give us a single place to manage all the cases listed above.

[olabini]

All done.