[WIP] Implement Reactive IRS

[moshthepitt]

Fix: #517

This PR adds:

• Community Health Worker model
• Each Community Health Worker object has an associated location object whose level is "chw" which has Districts as parents

[moshthepitt]

District list:

CHW List:

District Map:

CHW Map:

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@ukanga I think this is mostly complete now.

What is left:

• Adding tests :(
• Review if it works as it should