Added Equi2Ico and Ico2Equi classes

[viacheslav-m]

Created icosahedron util for angle calculation.
Created Equi2Ico numpy and torch runners.
Created Ico2Equi numpy and torch runners.

[haruishi43]

@viacheslav-m Hey thanks for adding a new function!

Before I can merge your work, I'd need to test it out and write some test codes to make sure that those functions are running as intended.
I'd appreciate it if you could give me some demo codes showing how equi2ico and ico2equi work.

Glancing through your code, I don't see many formatting errors, but if you could run black and format it, I'd appreciate that too! I'll look through the codes closely later.

Thanks again.

[viacheslav-m]

@haruishi43 Hi! I am going to add comments for the code to become more clear. Also I can share with you my colab notebook with example of tests. I will be pleased to answer any questions you may have!

[haruishi43]

@viacheslav-m Okay, that would make understanding your code much easier since I haven't gone through papers for icosahedron transforms yet. I'd love to see some of the tests you did!