Set new individual ID allows for duplicate IDs/marked individual pages to be made

[goddesswarship]

Expected behavior
From the encounter page (/encounters/encounter.jsp), If a user enters an existing ID for their species in the Set new individual ID field of the Identity section, an error message advises the ID is already in use.

Current behavior
Users can inadvertently create an infinite number of duplicate IDs by assigning the same ID in the Set new individual ID for each encounter of that individual, resulting in multiple, unique marked individual pages (/individuals.jsp) with one encounter each.

Steps to replicate

1. Assign a new ID from the encounter page by selecting Set new individual ID
2. Find a second unidentified encounter with the same taxonomy as the previous one and set the same ID with the Set new individual ID field
3. Click on the Encounter of [Name] heading from each of the encounter pages. They will point to two unique URLs for the same ID with the respective encounter on each one

Community link
https://community.wildme.org/t/zebra-wildbook-customised-animal-id-can-potentially-be-duplicated-to-more-than-one-individual-can-this-be-solved/4744

[goddesswarship]

Reported in Zebra Wildbook, but verified bug in QA.

[goddesswarship]

@holmbergius Pretty sure this is the cause of those mystery duplicates we couldn't find a root for.