Adding css reloader - #2852

The code changes the global GTK app state from a thread, which is not safe.
It also creates an inotify instance; that is a limited resource, and Waybar already creates way too many :(

Have you considered using Gio::FileMonitor or the underlying g_file_monitor instead? That would address both points.

Also, please consider adding a flag to disable the file watcher or even make it opt-in.

Updated with the changes suggested above.

LGTM, thx to both of you!
Can you add this new option to the man and github wiki? 🙏

I added the man page entry and edited the wiki.

Can you check the CI, freebsd seems to fail @dpayne

I believe I fixed the compilation error in freebsd, it was an issue with a missing import that only errors out on clang. I do not know why it hung after. It did seem to compile, this is from the workflow logs

[338/339] Compiling C++ object test/waybar_test.p/.._src_util_css_reload_helper.cpp.o
[339/339] Linking target test/waybar_test
1/1 waybar / waybar OK              0.12s

Ok:                 1   
Expected Fail:      0   
Fail:               0   
Unexpected Pass:    0   
Skipped:            0   
Timeout:            0   ```

LGTM, thx!
CI will rerun on master and timeout should be good