Re-implement searching for collections by spatial/temporal extent

[christophfriedrich]

When removing the Search section (#42), this feature was lost. I think it's useful, so it should be re-implemented into the Filtering feature of the Discover section.

However, a couple of things need to be considered for that:

• The filtering (so far) happens entirely on the client side. Having the extents of 1000+ collections available is another big chunk of data that has to be transferred and kept in memory.
• Only distinct collections are being returned, i.e. if multiple collections (across different versions of the same backend or across different backends) share the same ID, only the data (which, at the moment, consists of just the title attribute) of the first of them is returned ("first" as determined by MongoDB). This is not very problematic with titles IMO, but it may be more problematic if extents differ.
• How should it be integrated into the UI? I think I'd prefer an expandable area under the "Collections" heading.

[m-mohr]

• The filtering (so far) happens entirely on the client side. Having the extents of 1000+ collections available is another big chunk of data that has to be transferred and kept in memory.

I guess filtering is done asynchronously. So you could also mix client-side and server-side filtering, even considering multiple collections with the same name. For "large data" filtering, you could have an endpoints which takes a bbox and/or temporal extent and return all suitable collections ids, for example. In general, having a full server-side filtering API would be nice at some point.

• How should it be integrated into the UI? I think I'd prefer an expandable area under the "Collections" heading.

Agreed.