[~] fixed warning in featuers2d under windows (can't generate assignment operator)

minor fixes in CvGBTrees, its test and sample

converted user guide & tutorials from tex to rst; added them into the whole documentation tree; added html_docs target.

fixed compilation under Win64

Made changes in Android camera classes: now we can get list of possible preview resolutions of Android camera (as string).
Also now work of Android camera is more accurate in the case when the size of grabbed frame buffer does not consist with the expected frame size.

added missing cudaSafeCall