WebStyle: new /goto URL handler
WebStyle: new /goto URL handler

* Introduces new /goto URL handler. This is a plugin-based
  framework for URL redirectors, allowing a per-user
  registration of URLs under /goto/ path that will dynamically
  resolve to a final URL based on pluggable algorithms.

* Implements three plugins:
    * goto_plugin_simple, to implement a simple URL shortner;
    * goto_plugin_latest_record, to redirect to the latest record
      in a given collection or query;
    * goto_plugin_cern_hr_documents as an example of complex
      plugin that is used at the CERN Document Server.

* Implements the gotoadmin CLI.
  (closes #1178)

* Merge note: amended tests and left two of them in FIXME state.
  Need to touch them later.

Signed-off-by: Tibor Simko <c7116e45300b163846dc01f3ed02116e3f8ef7a5@cern.ch>

inveniosoftware/invenio-base,tiborsimko/invenio-base,tiborsimko/invenio-base,inveniosoftware/invenio-base