Build fixes - Githubissues

This PR includes build fixes needed to get Mintcoin to compile on a modern-ish system.

Most of the problems come because Mintcoin uses the OpenSSL 1.0.x API, and this was changed in incompatible ways for OpenSSL 1.1.x.

Notes:

This PR will break builds on older systems. It has been fixed in a subsequent PR, but I wanted to keep this PR separate for review purposes.
There are a lot of changes, but most of them are trivial. Code review would be much appreciated.
It makes me scared that there are no automated tests, but that is the world we live in.

MintcoinCommunity / Mintcoin-Desktop-Wallet