Upgrading to Catch2

[dcoeurjo]

PR Description

Upgrading the unit-test framework to Catch2 (https:/catchorg/Catch2)

Checklist

• Unit-test of your feature with Catch.
• Doxygen documentation of the code completed (classes, methods, types, members...)
• Documentation module page added or updated.
• New entry in the ChangeLog.md added.
• No warning raised in Debug cmake mode (otherwise, Travis C.I. will fail).
• All continuous integration tests pass (Travis & appveyor)

[rolanddenis]

Since I still had some comparison failures in testRealFFT, I have replaced the margin by a scale defined from the compared values. I hope it will work!

BTW, in the previous version of Catch, the scale was defined to 1 by default (see https:/DGtal-team/DGtal/blob/master/tests/catch.hpp#L2644).

[rolanddenis]

Merging, thanks!

[dcoeurjo]

🎉 ;)