Allow removal of removed triangles
Fix Unit Test
Merge branch 'feature/multi-triangle-removal' into 'master'

Remove the assert on double triangle removal

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/1124223
Revise UnitTests
Roll back changes in OsgGroup
Revise documentation
Update serializable stapling demo
Merge branch 'master' into feature/graphics-remove-visibility-property