add __contains__ method
update visual test runner for standalone tests
xml test styles standalone
Merge pull request #2602 from mapycz/standalone-tests

Standalone visual tests
Merge branch 'master' into image_data_any
move image_scaling traits into separate header to enable code sharing
c++11 - use constexpr
image_scaling - re-factor set_scaling_method for re-use accross code base
fix nasty typo + refactor more
remove redundant case
refactor warping code to work with different pixel_types and minimise code duplication