notifications: improve response time when number of notifications is large NotificationsController always retrieved materialized list of all notifications in database, even to display only 10 of them. This is improved by feeding SQLAlchemy Query object directly to webhelpers.paginate.Page, avoiding eager load of all notifications.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
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