Discourage overwriting an impl

[Deleplace]

Often, users click "Edit impl" and then write a very different implementation in the code snippet textarea. In this cas, they should have created a new implementation alongside the existing one, instead of overwriting it.

Please implement the following prompt:

IF the user clicks [SAVE] in the Impl Edit form of an existing impl, AND the user has modified the code snippet AND the modification of the code snippet is substantial (e.g. diff>5 characters) THEN display a new popin prompt containing

• old code snippet on the left
• new code snippet on the left
• "Are you fixing a bug in the implementation, or writing a different implementation?"
• Button [Fix existing implementation (overwrite)]
• Recommended button [Different implementation (create new)]