use maximum instead of max to filter for nil
Merge pull request #867 from YaleSTC/848_category_nil

Resolves #848, allows adding to cart with unlimited reservation lengths
convert datetimes to date for proper calculation
account for system time zone in calendar js
purge all resets all cart fields
empty cart uses ajax and js template
trigger pause cart when cart is emptied
format response
Merge pull request #877 from YaleSTC/876_overdue_fine

resolves #876 on v3.4
Merge pull request #884 from YaleSTC/883_fix_calendar_edge_case

resolves #883 for v3.4
Merge pull request #887 from YaleSTC/845_empty_cart

resolves #845 for v3.4
Merge pull request #870 from YaleSTC/868_emails_broken

resolves #868 in v3.4
Revert "Fix email links"
Merge pull request #891 from YaleSTC/revert-870-868_emails_broken

Revert "Fix email links"