[#673] Fix filter drop-downs for Pages site using keywords

When a Pages site uses keywords to populate performace issues preclude
filtering the datasets used to populate the filter drop downs. This fix
reverts so that the filters are populated using the full datasets when
the site is keyword driven.

To enable this fix the middleware now adds the current partner_site to the
request so it can be determined if the site is keyword driven or not.
[#671] Use relevant projects for partner site global map

Fix the map on the partner site home page so that it uses the actual
queryset of projects for the site instead of all projects associated
with the parter site organisation.

This is needed now that the projects may be selected based on keywords
rather than org association.

Conflicts:
	akvo/rsr/templatetags/maps.py
Merge pull request #676 from akvo/hotfix/673_pages_filtering

[#673] Fix filter drop-downs for Pages site using keywords