Adding in a new base class to support metrics

MetricBase provides a base class to support metric development. New
metrics should derive from the base class and redefine doTest() and
doMeasurement() ensure the system is ready to be measured and to perform
the measurement respectively.
Commit the responses to the merge request

This commit takes care of most of the code changes to the base files with
the exception of renaming this class SamplingMetrics and providing testing
code. These additional changes will follow.

The MetricBase class was renamed to SamplingMetricBase to allow for the
possibility of a superclass with additional metric functionality such as
reasoning on a series of measurements or of making broader go/nogo
decisions.

Added in unit tests to test the SamplingMetricBase class. The tests use an
additional mock class defined in MockObjects.h and required some (minor)
refactoring of the SamplingMetricBase class.
Merge branch 'master' into feature/metrics
Removing minor compile warnings

Broader testing on the build bot highlighted several compiler warnings.
This checkin (hopefully) removes them.
One more warning

Change the constant in the EXPECT_LT to be unsigned.
Turn on cpplint check for virtual and override

Turn on the cpplint check for looking for member functions declarations
that have both virtual and override. This is redundant, and we decided
to remove the virtual when override is present. Also, fix all the
occurances of this in the code.
Minor clean up of comments and style

This commit comprises largely stylistic modifications in response to Version 3 of the merge request.
Merge branch 'master' into feature/metrics
Merge branch 'master' into feature/virtual-override-style

Conflicts:
	CMake/SurgSimUtilities.cmake
	SurgSim/Physics/Fem1DRepresentation.h
	SurgSim/Physics/Fem2DRepresentation.h
	SurgSim/Physics/Fem3DRepresentation.h
	SurgSim/Physics/MassSpringRepresentation.h
	SurgSim/Physics/UnitTests/MockObjects.h
Merge branch 'feature/virtual-override-style' into 'master'

Enable cpplint inheritence checks (override/virtual)

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/1363803
Merge remote-tracking branch 'origin/master' into feature/metrics
Merge branch 'feature/metrics' into 'master'

Adding in a new base class to support metrics

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/1340683