khal interactive: set terminal title

[ddevault]

https://tldp.org/HOWTO/Xterm-Title-3.html

[WhyNotHugo]

What title(s) do you expect to see?

[ddevault]

Simply "khal" would be sufficient

[WhyNotHugo]

Keep in mind that you can configure a shell to do this for all commands.

E.g.: for zsh:

preexec () {
  print -Pn "\e]0;$TERM [%~]: $1\a"
}

This seems like a good idea anyway. The simplest approach with Python is:

print('\33]0;khal\a', end='', flush=True)

I don't think there's a single entry point where we can add this though, there's a few different ways to enter interactive mode.

That the title would remain as khal after we exit, unless we explicitly set it back to "", probably with atexit.