Add System Set Filters

[Zeenobit]

This is a PR to address Issue #26

I've added a new include_system_set member to Settings.
Inside included_systems_sets, I'm checking this mapper to skip any unwanted system sets.

I think the logic inside included_systems_sets could use a bit of clean up, but it seems to be working correctly based on my testing.

I've included print_schedule_graph_advanced_filters.rs as an example/test.

[jakobhellermann]

I'm not sure this is working as expected, shouldn't this only include the special systems with that filter?

[Zeenobit]

Did you test this with Bevy 0.14 or 0.15? I wrote this a few months ago. I wouldn't be surprised if it no longer works with Bevy 0.15