Map Query API + zooming to features returned to query

[ahmadayubi]

When a feature is returned from a query, the given feature should be focused/zoomed into view. The webpage author should also be able to decide whether a queried feature should be focused or not, through some facility.

[Malvoz]

Related: #482.

[prushforth]

Also possibly related. A "Map Query API" should really just be a querySelector, I believe. The API for (one or more) features could be based on returning the extent of that set, which could be rendered by a mapml-viewer.fitExtent(extent), perhaps (the latter function doesn't exist yet, but I think it might have been / might yet be useful for development of Aliyan's client)