feat(palette): integrate icons

Related to bpmn-io/bpmn-js#148
chore(dependencies): update karma-bro -> karma-browserify
feat(ElementRegistry): add filter method and align names

This commit cleans up the elementRegistry API and adds a #filter method
that allows users to select drawn elements by a given predicate.

Related to bpmn-io/bpmn-js#153

BREAKING CHANGE:

* The public api has changed:
* #getById, #getByGraphics have been combined to #get
* #getGraphicsByElement was renamed to #getGraphics