Use gmx_mtop_t in selections, part 1

Use gmx_mtop_t in selections, part 1

Make the C++ analysis framework (and insert-molecules, which is also
using selections) use a gmx_mtop_t as the initial internal format to
load the topology, and make SelectionCollection::setTopology() use an
mtop.  Adapt tests.  One test is disabled as it is much easier to
re-enable it after the next step in the conversion process than in this
intermediate state.

Internally, the mtop structure is still converted to t_topology for use
in lower levels and in the tool code.

This change also makes it possible to convert the analysis tools and gmx
insert-molecules to use gmx_mtop_t independently from changes in the
selection code.

Part of #1862.

Change-Id: I3ce03c6524b27f0f44168890ac1a4a491da52a4c