WebStyle: 1st commit of Flask-Invenio bridge
WebStyle: 1st commit of Flask-Invenio bridge

* New Flask-Invenio bridge to serve web request via Flask.

* Ports Invenio page layout to Jinja2

* Implements Flask blueprint support via pluginutils. Every
  handler will be implemented as a blueprint using
  dedicated Invenio decorators.

* Support for I18N, navtrails.

* Invenio session is shared between Invenio web handler and
  Flask handler.

inveniosoftware/invenio-access,tiborsimko/invenio-access,inveniosoftware/invenio-access,tiborsimko/invenio-access