SG-36193 Adds named filter support

[pscadding]

Adds support for creating more complex filters shown in the filter menu as a preset filter.
This mimics the web UI behaviour in part, although there is no ability to modify the filters from the UI, only toggle which one is used.

There is a separate PR for the panel app listed below and the changes here to the framework are implemented to allow support for the panel app to work. I don't believe any of the included changes would work against implementing this in other apps like loader2 or breakdown app 2, but there would be further work needed to support those apps such as:

• saving the state of the active preset filter
• handling docked filter menu mode.

I did do some work into getting it to work in the loader, and had implemented the state storing but I've removed it due to the loader implementation becoming more work on the loader side.

Panel app support is added here:
shotgunsoftware/tk-multi-shotgunpanel#97

I did look at making the preset buttons larger to match the other filter buttons but this became quite involved and in my opinion added unnecessary complexity for this particular use. From what I could tell I could either adjust the styling on all menu items, or I would need to create an manage a widget that gets applied to the menu so that I could style it individually.

[staceyoue]

@pscadding Looks good, but I do have a comment about refactoring how preset filters are handled. Let me know if it makes sense, or if you need any more clarification on it.

[staceyoue]

After more thought, the preset filters should remain as backend-filters (ideally the framework could handle this use case, but it needs a lot more work to do so).

Other than that, this is looking good, just a couple minor comments.

[staceyoue]

LGTM!