makes spec simpler and fix problem with leaking mocks
add referral_link only if referral_link is nil in session
Creates helper method render_project to render project partial with ref parameter
Adds ref parameter to ProjectsController#explore rendering
Adds ref parameter to views of the home page, thank you page, channel and user profile
fix spec for contribution edit
Merge pull request #1019 from diogob/referral_links

Add referral links to project links inside catarse