Filter api

This plugin filters nodes and edges in a fancy manner:
- Define your own filters on nodes and edges using the `nodesBy` and `edgesBy` methods, or execute more complex filters using the `neighborsOf` method.
- Register multiple filters before applying them anytime at once.
- Undo any filter while preserving the execution order. 
- Chain all methods for concise style.

See the README, example code and unit tests for full usage.