Add nginx reverse proxy to apache in Vagrant VM

Accessible at port 9001.
Add gunicorn to Vagrant VM
Automatically start dev server in Vagrant VM
Docs: Explain changes to Vagrant VM
Filter by date range in Dasboard/Reporting, if provided
Fix several issues for Django 1.6
Adjust version dependencies for Django 1.6
Disable template timings toolbar panel
Add migration for NullBoolean field
Filter different reports properly
Offer wizard works with JSON session serializer
Add reordering products inside ranges
Fix PEP8
Clean range ordering

- Remove forgotten print statement
- Rename `RangeOrdering` to more generic `RangeProduct` (later we can
  add another fields that are not ordering specific)
- Use `display_order` rather than priority (we set the order using
  jQuery sortable, not bump priority of couple products)
Fix backwards incompatible changes
Add correct CSS for date picker

It was using a incomplete bootstrap-datepicker.css. I couldn't find a
better suited replacement, so just switched to an okay looking JQuery UI
theme.

Also switched to the minified version of JQuery UI.
Upgrade timepicker to current version

As part of reviewing datetime pickers, it seemed sensible to bump to the
current version.
Fix custom_range bugs with ugettext_lazy in custom range object name,
and unique fields error when creating existing custom ranges.
Fix for delegate of num_products to a proxy class as documented.
Reduce number of evaluated queries.

* Replace "foo.count() == 0" with "not foo.exists()" in python files
* Replace "foo.count() > 0" with "foo.exists()" in python files
* Replace "{% if foo.count %}{% for bar in foo %}" with
  "{% if foo %}{% for bar in foo %}"
* Use 'with' template tag in templates
* Add myself to AUTHORS list