Adds force & torque scaling device filter.
cpplint fixes for ForceScale: too-long line and trailing whitespace.
Put file-local constant in unnamed namespace in ForceScaleTest.
ForceScaleTest tests the default scaling.
Merge branch 'master' into feature/devicefilter-forcescale
Merge branch 'feature/devicefilter-forcescale' into 'master'

A device filter that scales output forces and torques.

+1: Julien Lenoir, haizhouW, gsathyaseelan

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/783133
Serialize StapleElement
UnitTest for serialized StapleElement.
Make StapleElement as a library, so that FrameworkConvert can create it.

Also, updates CMakeFiles in other UnitTests, to make build successful.