WebAccess: ORCID support
- Introduces support for OAuth2-based ORCID authentication by exploiting the external authentication support to OpenID/OAuth1/OAuth2 introduced with the previous commit.
- Amended previous commit by cleaning up INSTALL guide and root-level Makefile.am, introduced configuration of providers in invenio(-local).conf.
- In the previous commits, the new provided plugins were implemented assuming to be instantiated per-every request, while each plugin is instantiated only upon server loading and can't hence share request-oriented information. For this reason a new attribute called "g" (mimicking upcoming Flask global "g" proxy) to the req object. (closes #1124)
Tested-by: Tibor Simko <tibor.simko@cern.ch>