* Generate field names with brackets when needed.
* Stop hard-wiring complex selectors as `["field1", "field2[sub-field3]"]`
and instead represent them as a more consistent `["field1", "field2", "sub-field3"]`
* Convert all filter strings ending with square brackets to an array.
Stop special-casing 'metadata.labels[X]' and handle any query string that ends with '[...]'.
* Stop checking for pre-bracketed terms in constant field-accessor arrays.
In this commit we stop converting string arrays like
`["metadata", "labels[k8s.io/deepcode]"]` into the database field
`"metadata.labels[k8s.io/deepcode]"` and instead will do a
naive `join` to give `metadata[labels[k8s.io/deepcode]]`. The solution
is to never express the above terms in separate fields, like
`["metadata", "labels", "k8s.io/deepcode"]`. This also better reflects
the stucture of the referenced object.
* gofmt changes
* Simplify comment about 'smartJoin'.
