Add id to filter fields for children-api endpoint

[MrApplejuice]

Background

The api endpoint http://localhost:8888/api/children/ right now uses the slug of a child to do a detail query, while most filter-options for activities (tummy-time, use the child-id to implement filtering.

I have encountered a bug in the Android App I am developing for which it would be handy to do a quick check for the existence of a child. It is kind of awkward to have to use the slug for this while I use a child-id for all other types of queries.

Solution

To allow for a quick "exists"-check against the database, I added the "id" flag to the filterset-fields to allow http://localhost:8888/api/children/?id=xxx which will solve this issue. Less awkward than traversing a potentially super-long list of child-items just to find the one you are looking for...

[coveralls]

Coverage: 99.018% (-0.04%) from 99.055% when pulling e613f4d on MrApplejuice:add-child-id-to-filter-fields into 77d4ba1 on babybuddy:master.