Beefing up wallet server to support evidence-collection graph and MRTD chip reading

[sorotokin]

Major changes:

• support for evidence-collecting graph on the server
• support for NFC tunneling to read ePassports/cards Minor (supporting) changes:
• move from (mutable) ByteArray to (immutable) ByteString in evidence request/response datastructures
• made a pass through sever storage code to support MySQL in addition to HSQLDB
• generic facility to cache objects created from configuration and resources

Fixes #624

Tested manually both using in-app server and local http server (including with MySQL database)