This allows the user to apply and/or validate a manifest using
either a filepath (as before) or URL.
Addition by sh8121att:
- Create a general document resolver class to handle local paths
and URIs
- Allow multiple filenames and combine them into a single document
set
- Change API to allow for passing document reference URIs to be
resolved server-side rather
- Update validation API to conform to UCP specification
- Dockerfile updates to speed up build
- Fix unit tests
Closes #96
Change-Id: I5a57779f10d1b63ffc161a14afec851a34ae9efe
d383e772fd