Feature priorities

[chenkasirer]

• Features have now priorities (workaround for nasty issue applying certain brep subtractions before trimming)
• Beam.attributes now gets serialized.

What type of change is this?

• Bug fix in a backwards-compatible manner.
• New feature in a backwards-compatible manner.
• Breaking change: bug fix or new feature that involve incompatible API changes.
• Other (e.g. doc update, configuration, etc)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I added a line to the CHANGELOG.md file in the Unreleased section under the most fitting heading (e.g. Added, Changed, Removed).
• I ran all tests on my computer and it's all green (i.e. invoke test).
• I ran lint on my computer and there are no errors (i.e. invoke lint).
• I added new functions/classes and made them available on a second-level import, e.g. compas_timber.datastructures.Beam.
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

[obucklin]

Should FeaturePriority be an int instead so we can set the order in case of multiple overlapping features?

[gonzalocasas]

I think it is already one, even if there's a class to wrap it, it's only acting as an int enum.

[chenkasirer]

@gonzalocasas @obucklin I'm gonna close this one for now as this was more of a workaround and I'm not so happy about this solution. If I see there's no other way, I'll open it again.