[#268] Add Piwik analytics

Add django-piwik to requirements

Add settings for Piwik

Add template tags in rsr/base.html and partner_sites/base.html for Piwik

Conflicts resolved in:
	scripts/deployment/pip/requirements/2_rsr.txt
[#268] Add Piwik template tags to widgets
[#251] Changed form text from 'Add update' to 'Submit update'.
[#216] Changed string "water and sanitation" to "development aid".
[#215] ISO country string changed for country code PS.