Xcursor linking error on mac builds

[jakoch]

libxcursor-dev is installed, but lib is not picked up: ld: library not found for -lXcursor,
see https://travis-ci.org/fifengine/cpp-tutorials/jobs/164026624#L1168

• add finder
• use finder in cmakelist

[jakoch]

Lib is there and found: https://travis-ci.org/fifengine/cpp-tutorials/jobs/164078058#L1114
But not linked: https://travis-ci.org/fifengine/cpp-tutorials/jobs/164078058#L1165
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