starting on spatial locator and tree testing.

Element evaluation:
- for tets, change the reverse evaluation strategy: changed to 25 iterations, and start from
  nearest vertex
- fixed a bug in original reverse evaluation implementation
- added an inside function that returns whether a given parameter is inside the element; for some elements
  (i.e. tets), there isn't necessarily a fixed upper value for all parameters
- fixed handling reverse evaluation function to allow particular element types to substitute their own evaluator
  function (and use this for tet evaluation)
- spectral quad, hex: use inside function instead of duplicating code to directly evaluate it
- in elem_eval_test, for integration test, create a tag with value 1 on vertices to compute volume;
  also fixed bugs in iteration over multiple elements

Spatial locator/trees:
- changed delete_tree to reset_tree
- enabled some things for structured mesh that weren't before
- added test/spatial_locator_test.cpp
- in SpatialLocator, add code to initialize tree if one isn't input

Other:
- in ScdInterface, if applications don't input coordinates, compute them from parametric space
- fixed some compile warnings in MBZoltan