WebSearch: add download graph to record blueprint

* Add download graph to template context to match functionality
  of previous Invenio versions.
InvenioUpgrader: partial fix for SQLAlchemy init

* InvenioUpgrader imports pluginutils which imports webinterface_handler
  which in the end results in an SQLAlchemy model being imported. The model
  then raises an exception due to the SQLAlchemy engine not being initialized.
  This partial fix ensures the engine is initialized by loading
  invenio.flaskshell. However, 'make check-upgrade' will not work for
  non-SQLAlchemy based installations, but will nonetheless report this.