BBOX Validation

[Nmargolis]

A GET request with an invalid bbox to the /api/data/features/endpoint currently returns a 500 error.
For example: http://localhost:8888/api/data/features?bbox=badbbox

It might be nice to have some validation of the bbox parameter and get a 400 response if the bbox isn't in the expected format.

Not sure where the server is erroring out, but maybe here? /src/lib.rs#L460

cc: @mattficke