Support for registrations by SMS

Server

Important: server requires database schema update

Support for registrations and password recovery by SMS. The only missing part is the actual adapter to call Twilio or Sinch or some such.

Other features:
8a4484e Enable compression of websocket frames.
67a6af7 Update Docker with gc of stale accounts, google analytics, send validation methods to clients.
d22bb79 Add timeout for KeepAlive connections.
d5bcb4c Allow disabling of account deletion by ordinary users, #836
4366da4 Python gRPC regenerated

Bug fixes:
9f9d8de Fix incorrect unread count in user cache.
eac88f6 Fix CORS handling, #840.
001a35d Hard-delete incomplete user records (was soft-delete), #839.

Tindroid

https://github.com/tinode/tindroid/releases/tag/v0.22.0

Tinodios

https://github.com/tinode/ios/releases/tag/v1.12.0

TinodeWeb

https://github.com/tinode/webapp/releases/tag/v0.22.0

JS SDK

No material changes