Implement symmetry reductions

[muodov]

The current implementation is a direct translation of Kociemba's twophase.jar, which is the two-phase algorithm in its simplest form. On his page, Herbert describes further possible optimizations that can improve the algorithm performance, e.g. symmetry reductions.

He have implemented those in his Cube Explorer program, but unfortunately that source code is not publicly available. So we'll have to implement it ourselves.

[muodov]

For the algorithm details, see http://kociemba.org/cube.htm

[xanxerus]

https://github.com/hkociemba/CubeExplorer