Fix compositing performance (3x improvement)

[BurkusCat]

How to test

Comment out tickRelationshipOutlines(); in neo4jd3.js like this:

            tickRelationshipsTexts();
            //tickRelationshipsOutlines();
            tickRelationshipsOverlays();

This removes other bottlenecks. Compare the performance of dragging around icons before vs after this change.

Before (75ms total task time~, around 50ms is compositing):

After (25ms total task time~, around 1ms is composting):

Reference: https://stackoverflow.com/a/40533907/3991315

[BurkusCat]

Improves #8

[Trufflegator]

Looks good, will keep an eye out for if anything breaks.