Refactor using of crypto functions

[g1itch]

In this branch I'm gonna cover by tests all the crypto functions used in code and do a refactoring. Basic points:

• only highlevelcrypto should import from pyelliptic
• highlevelcrypto should not depend on the app state e.g. module state or BMConfigparser() instance (the same will be done for protocol in #1788)
• highlevelcrypto should include hashes - double sha512, ripemd160
• finally I'm gonna detach pyelliptic into the separate repo to show a possible way of addressing #886

[PeterSurda]

overall nice work, although I haven't investigated it in depth

[g1itch]

overall nice work, although I haven't investigated it in depth

It seems that I misplaced (or misnamed) the signatures. I was going to regenerate them. And there is also a lot of unfinished changes here, mentioned in the PR description.