WebSearch: add bibdocs to record context
installation: initial upgrade recipe for next

* Create WebDeposit tables.
WebStyle: nice error page view decorator

* Add flask view decorator that will catch specific exceptions and
  render a nice error page for the end-user. The decorator is
  complementary to the normal Flask error handlers for 404 and 500
  HTTP errors.
WebStyle: customize Flask request class

* Adds InvenioRequest as the default Flask request class with methods
  to allow for easier Flaskification of legacy modules.
WebSession: fix typo in variable name
WebSession: port user registration to Flask

* Ported user registration view to Flask but moving register view from
  websession_webinterface to webaccount_blueprint and creating a new
  WTForm form with validation logic for user registration.

* Use email instead of nickname for login

* Fix issue in webuser when dealing with Flask generated legacy
  requests instead of proper legacy requests.

* FIXME Unauthorized access page not ported
WebDeposit: fix pre_validate method in fields

* Ensure pre_validate function signature matches that of WTForms.
  Already fixed by Kostas, so to be removed from next-op once new
  WebDeposit changes have been pushed and integrated into next-op.
WebStyle: install I18N Jinja2 extensions

* Load Jinja2 I18N extension.
WebStyle: fix Flask request compatibility issue.
celery: Adds integration of Celery in Invenio

* Adds Celery support to Invenio by defining a custom Celery loader
  that will 1) load tasks defined in invenio.*_tasks modules, 2)
  ensure that the Flask application and request context is set so
  tasks can make use of e.g. SQLAlchemy.
WebStyle: fix bug in pageheader template

* Fixes a small issue which would case an exception when rendering
  certain pages.