Improved performance of computing HF and spectral sequence.

- braid.py: refactored functions on cobordisms. In closeCap, use
  morToD when genus is 3 or below.

- braidtest.py: benchmark for T(5,4) (using 5-bridge presentation) is
  ~250s. Benchmarks for T(5,6) is ~5400s and 6.5G of memory.

- extendbyid.py: overrode tensorD in dastructure with its own
  function. Incrementally keeps track of idempotent assignments, local
  restrictions, and product of outer restrictions, to avoid repeating
  any computations. Factored several functions that are used in
  tensorD, delta, and/or deltaPrefix.

- localpmc.py: restrictStrandDiagramLocal/Outer are now memorized
  within the strand diagram. This is with the expectation that the
  generation of strand diagrams (in PMC) itself is memorized.

- pmc.py: memorization of the construction of strand diagrams. Used in
  three places where strand diagrams are produced most heavily
  (multiply and diff in pmc, and joinStrandDiagram in localpmc).

- utility.py: added trace function. For debugging only.
Cleanup of braid.py. REMOVED CODE about arcslide fixes of ends. This
function is completely replaced by using cobordisms.