Add URN:NBN resolving

[Twan Goosen]

URN:NBN links are rewritten to links to the ​resolver (see #153, r5025). Functionality could be added to actually resolve the URN exactly as happens with handles. Simply adding a handler to UriResolverImpl.java will make this happen, since its resolve() method gets called via Ajax for resource links after page load.

The way to implement a handle would be very similar to the Handle API handler (HandleRestApiClient.java) except that the response of the NBN resolver is XML.

For example, to resolve the URN urn:nbn:de:gbv:23-drucke/814-4-theol-1s4, a request needs to be made to ​http://nbn-resolving.org/resolver?identifier=urn%3Anbn%3Ade%3Agbv%3A23-drucke%2F814-4-theol-1s4&verb=full&xml=on, which returns

<?xml version="1.0" encoding="UTF-8"?>
<!---
This is a computer generated response to your request listed below. Do NOT modify it manually!
In case of a problem see the XML Schema Definition (http://nbn-resolving.org/schemas/pidef/1.0/pidef.xsd) first.
Kadir Karaca Koçer - German National Library
 -->
<pidef:pidef xmlns:pidef="http://nbn-resolving.org/pidef" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://nbn-resolving.org/pidef http://nbn-resolving.org/schemas/pidef/1.0/pidef.xsd">
  <pidef:header>
  ...
  </pidef:header>
  <pidef:data>
    <pidef:resolving_information>
      <pidef:pi_info num="2001356488">
      ...
      </pidef:pi_info>
      <pidef:url_info>
        <pidef:url>http://diglib.hab.de/drucke/814-4-theol-1s/start.htm</pidef:url>
        ...
      </pidef:url_info>
    </pidef:resolving_information>
  </pidef:data>
</pidef:pidef>

Only the value at /pidef/data/resolving_information/url_info/url is of interest for this purpose.

[Twan Goosen]

Splitting 3.1 milestone. Most open tickets go to 3.2 so that we can have a release on the short term.

[Twan Goosen]

Removing invalid/wontfix/worksforme tickets from 3.2 milestone