Move to submodules and add run deletion endpoint

[GabeBolton]

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[istride]

This PR is one commit behind main, which may solve the problem that led you to use git submodules. Would you try that latest change from main? If it works, please remove the submodule stuff.

It is too difficult to identify which part of the code is original and which are our changes - this will make it difficult to maintain our changes across versions. My suggestion is that we isolate our modifications within a Django "app" and install it into RapidPro as a third-party package rather than overwrite existing code. That also means that we should segregate our API endpoints from the existing (temba) endpoints, so that it's clear which are official and which are not.

I can help with packaging up this IDEMS app - with our extensions in it - I would just need to have a clear idea of what changes you've made.