Add config reload support

[MartinPit]

Btop is now able to respond to SIGUSR2 signal and apply any changes made to config file, which were made while it has been running. Also added a key bind to do so manually.

This changes addresses my needs but also resolves #683.

• By supplying SIGUSR2 signal the config is reloaded from disk
• Pressing ctrl+r in app also does the same
• Help menu extended with ctrl+r entry

[imwints]

SIGUSR1 is already used to interrupt the key polling (? something like that).

[MartinPit]

SIGUSR1 is already used to interrupt the key polling (? something like that).

I don't think it is, because the line is currently commented out, no?

[imwints]

That is not commented out, this is just a comment what the signal is used for.

We have a couple of places in the code which will send SIGUSR1 to the process. This will now always reload the config.

[MartinPit]

Oh, my bad then. Would it be fine if instead it would be switched to SIGUSR2?

[imwints]

I guess so. Have you thought about making this a key bind instead?

[MartinPit]

I feel like a signal would be better, as I and also the author of #683 would like to use it as a part of an automated script when switching desktop themes. But, there is also an option of making both signal handler and a key bind.

[MartinPit]

Edited with suggested changes.

[aristocratos]

Thanks for contributing!