Move crypto package contents to the new plugin structure

Move the HSM-style crypto source modules into the new plugin structure, and
integrate this into the rest of the Barbican API and worker source flows, via
the secret-store to HSM-style plugin adapter store_crypto.py. Removed
crypto source and unit test files from the old locations.

Implements: blueprint restructure-for-plugins
Change-Id: Ie31531ac71a32b14598b903632e8a3127a263e56