Idea: refactor the Hifi prefix into H

[PaulRBerg]

Proposed new contract name: HPool instead of HifiPool, HPoolRegistry instead of HifiPoolRegistry.

This would:

1. Reduce the net total size of our code base (slightly).
2. Make the nomenclature consistent with the H prefix in the HToken.

[scorpion9979]

I think it should be noted that this would have absolutely no effect on the compiled bytecode, especially since we have the compiler configured to ignore the metadata hash. Therefore, any decision we arrive at here should be entirely in favor of dev UX and readability.

Reference: https://ethereum.stackexchange.com/questions/114858/is-the-solidity-contract-class-name-of-any-relevance

[PaulRBerg]

Very good point. I am still in favor of this refactor, FWIW.