Implement Query Definition Feature Filtering

[philipbaileynar]

Once we have definition queries in business logic. Need to implement them in ArcRAVE to filter features.

Related Issues

• Riverscapes XML query definition task
• ArcRAVE XML query definition task
• Early BRAT extent issue

To filter which features are included in a layer you use the setSubsetString() method on the QGIS layer object:

layer.setSubsetString(expr)

[KellyMWhitehead]

This was relatively easy and straightforward!

Added in dbadb62

[joewheaton]

We now have in Riverscapes/RiverscapesXML#333 a test case with BRAT.