fixed dependency of stitching module on xfeatures2d module as optional
fixed the initModule_xfeatures2d function that was called in module stitching since it is in another namespace than the standard cv one.

- Reworked documentation to reflect actual code
- Removed some unused variables
- Removed unnecessary 'cv::' modifiers

- Extracted common operations to separate functions.
- Activated first parameters set.
- Some output formatting.
- Fixed loop break condition in mini_batch_gradient function.

trying to solve compile problems; temporarily disabled some tests for just added optimization algo's

1. someMatrix.data -> someMatrix.prt()
2. someMatrix.data + someMatrix.step * lineIndex -> someMatrix.ptr( lineIndex )
3. (SomeType*) someMatrix.data -> someMatrix.ptr<SomeType>()
4. someMatrix.data -> !someMatrix.empty() ( or !someMatrix.data -> someMatrix.empty() ) in logical expressions