changed OpenCV license from BSD to Apache 2 license

[vpisarev]

Many files still contain old-style copyrights though.

See https://github.com/opencv/opencv/wiki/OE-32.--Change-OpenCV-License-to-Apache-2

Pull Request Readiness Checklist

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 Apache 2.0) License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to original bug report and related work
• [N/A ] 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