closes opencv/opencv#5506

Please don't merge yet. I will be adding test and sample code. @berak can you kindly have a look? I feel I am including everything but I get an error. OpenCV compiles perfectly (or so I suppose).

undefined reference to `cv::text::SWTTextDetection(cv::Mat const&, bool)' when I compile a sample program. The hpp file is loaded but apparently cmake or gcc cannot find SWTTextDetection.cpp. I have been stuck on this for two days now :/
I could confirm that SWTTextDetection.cpp is definitely being compiled by cmake.

This most definitely has something to do with SWTTextDetection.cpp not being loaded or linked during make.

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under OpenCV (BSD) License.
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• The PR is proposed to proper branch
• There is reference to original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

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