Refactor undistort step into a separate tool

[AlexeySachkov]

It is annoying to go through undistort step each time when you experimenting with cameras.

Calculating of distortion coefficients and camera matrices should be done only once per camera model.

This new tool should accept list of input videos and generate config file which can be used to undistort pictures produced by the cameras. Such config file should be accepted by stitch tool in order to skip undistort step.