Add Telegram Desktop

[abbradar]

Things done:

• Tested using sandboxing (nix-build --option build-use-chroot true or nix.useChroot on NixOS)
• Built on platform(s)
  • NixOS
  • OS X
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

More

Adds Telegram Desktop and required packages.

P.S.: In my personal rating of packages with completely crazy, "because f*ck you that's why" build sequences this would make a top, and for a long time I feel. The most funny thing is that, modulo several improvements for using more system libraries and more INCLUDEPATHs than expected (Because why use pkg-config? Let's just hardcode FHS paths for all packages we use and their dependencies by hand!), this is an official building procedure (see 1). Yes, with a statically built Qt with custom patches "because our font rendering engine uses internal Qt calls". Yes, with sed-patches and manual adding of LIBS to link to. Yes, with this grep ... | sed ... | xargs make -- because why spend time to figure out how to properly list dependencies in QMake? And even -- yes, with Arch AUR package as an official source for .desktop files.

Not a nice package, certainly. If you spot any profanity in the code, please excuse me -- I was forced.

[mention-bot]

By analyzing the blame information on this pull request, we identified @edolstra, @copumpkin and @peti to be potential reviewers

[7c6f434c]

I hope this line is a typo.

[abbradar]

Copy-paste error. Thanks, fixed!

[7c6f434c]

I hope pcre path didn't change in the pcre8 variant? Looks good to me.

[abbradar]

Yes, I've taken extra care to ensure plain pcre is not affected. Travis error is due to log growing too much. I'll merge this in several days to leave a window for review.

[astsmtl]

Official Telegram client doesn't support alternative input methods (like uim). It seems like this is due to the fact they use their own version of Qt. Do you have any idea how to fix this?

[abbradar]

We can try to patch it to use proper system Qt, but that can quickly turn tricky. See telegramdesktop/tdesktop#1815

[jagajaga]

cc @volhovm

[jgillich]

our font rendering engine uses internal Qt calls

Waow. Because a chat app is so complicated, of course they couldn't use the regular Qt API.