Wip/2.0 taxonomy refactor

This PR is to track `wip/2.0-taxonomy-refactor` branch related to #298 and #312 :

- [x] Rename table `nodes_taxonomies` to `model_taxonomies`
- [x] A new behavior (with methods from `Node` model to handle taxonomy specific processing)
- [x] Add handler for `Model.Node.beforeSaveNode` in `TaxonomicBehavior` to address issues raised in #298 
- [ ] Extract more Taxonomy specific code:
    - ~~`formatData`~~
    - `updateAllNodesPaths`
    - ~~`parseTaxonomyData~~ from `Nodes.Node` into Taxonomy plugin, most likely in `TaxonomicBehavior`
- [ ] Minimize dependency between `Nodes` and `Taxonomy`