Fixed up how taxonomy term page shows mixed content #4871

The _load_multiple and _view_multiple functions are cached and therefore faster than looping over a bunch of types/ids and loading each individually, which was how I approached things at first.  This commit uses those functions to load all entities, grouped by their type, then it collates the rendered entities according to the they were originally returned in.

This is done as generically as possible so we could list some other entity type here as well as files and nodes.

As I learned before, teaser is specified in all view functions.  Can't expected consistent defaults anywhere.

TODO: still checking that new term pages look just like the old ones, but with the inclusion of files.