Add tolerence to Triangle/Triangle Intersection test.

- To avoid false positives.
Adjust epsilon to pass unittests in linux 32.

- New values got by trial and error.
Rephrase the test for triangle intersection + Add more comments

- Now the test ensures that the projection of both the triangle on the separating axis is at least a line segment and then proceeds to check if they overlap.
Merge branch 'master' into fix/linux32-unittest-failure
Merge branch 'fix/linux32-unittest-failure' into 'master'

Fix linux32 failing unit tests

+1: Ryan Beasley, Paul Novotny, Wesley Turner, Julien Lenoir

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/1310923