Some issues with experiments

[oscgonfer]

• Experiments shouldn't allow for dup kits:

• In @peters-rebecca's computer, we add kits to an experiment.. (nothing shows up on the search bar)
• If a reading is not present, we get a 500 when visiting https://api.smartcitizen.me/ui/experiments/29/readings?measurement_id=71 (not always - needs testing)