ale::States implementation (#314)

* Adds an initial header file for the States

* Small updates to State header re: disucssion about not including units

* Adds most of an implementation and tests for just the constructors

* Actually add tests

* Adding tests for all except reduceCache

* Adding in tests for minimizeCache

* Add rough draft of minimizecache to states

* Update error throws and a bit more cleanup

* Clean up weird way I was creating vectors of states for tests

* Restore Lauren's test data values

* Add tests to bring test coverage up

* Fix tests I didn't test before pushing up

* Update for review comments 1

* Make other updates based on review comments

* Update to make minimizeCache return a new States object and change a lot of function signatures to use const references for vectors

* Move interpolation-related utils out of States into ale.h and update tests appropriately

* Updated state interpolation to reduce needed times

* Changed the position and velocities in the test fixture to values from functions

* Updated the spline interpolation to use the interpolation subset

* Removed parenthese again

* Added tests for vector size checks

* Addressed PR feedback

* Removed the interpolateState function as it was a copy of interpolate function

* Updated States to use interpolate and not interpolateState

* Removed interpolateState tests

* Updated state tests

* Removed interpolateState from ale header

* Updated interpolation tests

Co-authored-by: Adoram-Kershner <ladoramkershner@igswzawglt0046.gs.doi.net>
Co-authored-by: Jesse Mapel <jam826@nau.edu>
Co-authored-by: Adam Paquette <acpaquette@usgs.gov>
Co-authored-by: Jesse Mapel <jmapel@usgs.gov>