Generic gmx check implementation with KeyValueTree

Generic gmx check implementation with KeyValueTree

Implement gmx check as a generic comparison of KeyValueTree objects,
instead of calling IInputRecExtension.  This removes all special code in
the modules needed to support gmx check.

Only bare minimum comparison functionality is implemented for now to
support the cases that are possible with the electric field module.

Change-Id: I2b9a025c61022919f1c6730b9523983416d08364