Backport changes from upstream (1.2.17)

[crackedmind]

[berkus]

• Define a procedure for pulling necessary changes from upstream.
• Document it.
• Make a list of changes we need.
• Pull changes we need.

[leha-bot]

I suggest the next procedure:

1. Sometimes fast-forward the upstream-master and upstream-dev branches in our repo (for example, every release or on demand);
2. If we need some features from upstream, we just cherry-pick it, if available or create an issue with label sync and related) with link to commit(s); If we created an issue, then follow the berkus' plan (from 2nd paragraph)

[berkus]

Tracking branches upstream-dev and upstream-master sound good!

[leha-bot]

https://github.com/telegramdesktop/tdesktop/commit/dc9483e07a752d07b7e01836dfdbbd37304a80bb Deadlock Fix from 1.2.17. We should check our code for this bug