Enhancements/Bug fixes for prokaryotic summary visualization project

[ThHarbig]

This issue tracks all issues related to bugs that need fixing or useful enhancements for the prokaryotic summary visualization project.

Bugs:

• Brush display in stacked tracks in circular layout Brush in circular layout with stacked tracks #885
• Displacement type pile does not work Displacement type pile with overlaying tracks does not work #883

Enhancements:

• Create API to support summary visualizations in gosling API to support utility visualizations in Gosling #895
• Improve ways of gosling to communicate with the outside world Raw data event improvements #894
• Metadata concept in gosling.js/gosling-meta.js Metadata concept of gosling/gosling-meta #925
• Placeholder views Dummy/placeholder track/view #924
• Make higlass view specs invisible in API Gosling - Higlass track API improvements #909
• Unify brush track and rangeSelect mouse event Idea: Unify brush and rangeSelect mouse event #910

Wishlist (enhancements that would be nice to have for the examples that I implemented):

• Overlaying single tracks across multiple tracks Overlaying a single track over multiple tracks #884
• Reducing number of data redefinitions Root "data" or "datasets" #508
• Click to change brush position Click on track to move brush to clicked position #889
• Clockwise orientation of circular layout Is it possible to change the orientation of circular tracks? #280
• Advanced triangle shape Arrow with tip of arrow = end of feature #905
• clockwise orientation of circular layout Is it possible to change the orientation of circular tracks? #280