Make type and ou choices required in new role form

Adding a role without selecting either of these makes no sense, and will be refused by the backend accordingly.

frontend/public/locales/en/common.json

@@ -116,6 +116,8 @@
     "invalidEmail": "Invalid e-mail address",
     "passportNumberRequired": "Passport number required",
     "mobilePhoneRequired": "Mobile phone is required",
+    "typeMustBeChosen": "Role is required",
+    "ouMustBeChosen": "Organisation is required",
     "startDateMustBeSet": "Start date must be set",
     "startDateMustBeBeforeEndDate": "Start date has to be before end date",
     "phoneNumberAndCountryCode": "Both country code and phone number must be set",