Overrides taxonomy_term_page with custom page and campaigns, view for #3159
Fix source URL
UK SSO: adapt login/signup to common flow provided in external_auth.
Adds source=campaigns to query string DS-388
Merge pull request #3172 from aaronschachter/term_tpl

Custom taxonomy term page
Merge pull request #3173 from aaronschachter/source_campaigns

Appends source query string to /campaigns
Changes per #3174 review.
Merge pull request #3174 from sergii-tkachenko/DS-379_uk-common-auth-module

UK SSO: adapt login/signup to common flow provided in external_auth.