LIBSLIC3R: Port tests to CATCH

[lordofhyphens]

As a software developer of libslic3r, I want libslic3r's existing tests to execute without requiring Perl or XS, so that I can be alerted when my changes break something in libslic3r and I've already uninstalled Perl.

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As of cdb9d61, we have CATCH available to us in the src/test dir.

Please put libslic3r tests in ./src/test and update CMakeLists.txt accordingly.
New cpp files should be added to SLIC3R_TEST_SOURCES