use centroid and line testing options

Description: right now when testing membership of a svg element to a split we use its bounding box. It will be interesting to see how using its centoid as a point would compare. There may also be some performance boosts (speed).

To recreate robins experiment we also want to use a horizontal line through the centroid.

ACCEPTANCE CRITERIA:

• implement points and horz line for testing.
• have default be bounding boxes, only test as point or line if specificed in phoc spec
• Do benchmarking to assert how they compare speed wise
• modify visualization methods
• write some tests