Upgrade path for this plugin

[ehildenb]

There are several changes that need to be made to facilitate (i) modularity of the KEVM build, and (ii) hooks needed by the Michelson Semantics.

Here is the proposed upgrade path:

1. add some new hash functions that Michelson needs

• add a libcrypto++ submodule so that we can still do test builds in this repo --- because the libcrypto++ package in Ubuntu/Debian doesn't include the needed symbols
• add the hash functions blake2 and sha2-512

2. upstream the KEVM hooks/build recipes

• add all KEVM hooks to the plugin
• hide the Michelson hooks that depend on a more recent version of libcrypto++ behind a tangle tag
• make KEVM source the plugin hook file and delete its internal copy of the hook file
• upstream the KEVM build recipes for its crypto submodules and directly call the plugin Makefile build recipes

3. split out the hooks in build plugin file into separate modules based on which library they use

• update the plugin hook files and build test (also update plugin hook names, refer to add new hook names for crypto hooks k#1216)
• update KEVM so that it sources the new files correctly

[sskeirik]

First phase is finished and ready for review #104.