Switches select_all_search_results to new Cart interface. Add a corresponding spec for testing the functionality of "Select all". Introduce VCR for fast/low maintenance API testing, as this spec will call Solr 20x times. Fixes #58.
Ignore localhost for VCR
Stop querying Solr with increasing offsets after there are no more results returned. This used to always go up to article limit, regardless if the search returned 3 results or 3000.
Simplify paging logic by only allowing current_page to page, and not 'start'. Fix Select All for CrossRef too. Fixes #58
Merge pull request #70 from articlemetrics/select_all

Fixes "Select all" functionality