Added string matching function.

This is extracted from PathMatcher and will be used as the basis for unifying string matching across Gaffer as required by #707.
Added numericSuffix() function to StringAlgo.h.

This allows us to remove some duplicated code from GraphComponent and BranchCreator.
Added a Duplicate node to GafferScene.
Merge pull request #794 from johnhaddon/duplicate

GafferScene::Duplicate