Add CitySDK exporter

Export categories, places and events with '$./manage.py event_export CitySDK --new'
Delete exported from target system  '$./manage.py event_export CitySDK --delete'
Add minor refactorings and pep8 fixes
Merge commit 'a9f64d2c8f4102cb7806390b7c214f1771247790'

Also added simple client HTML for API event search

Conflicts:
	linkedevents/settings/base.py
Merge commit '50d838f9a3e34ab8b3da83e3f1862d3a4101fc89'
Add Helmet importer
Add support for recursive page fetching
Cleanup some code
Simplify the search form and add pagination
Merge branch 'master' of https://github.com/City-of-Helsinki/linkedevents
Add improvements
Fix currentPage reset bug
Fix pagination bug
Add export.sh, add HelMet to import.sh
Fix CitySDK issues

It's not necessary to move _all_ categories and places, just those referring to events
Add sanity check for expired session
Add better language support