fix wrong property name and corresponding documentation

Simply said

- The property CV_CAP_PROP_WHITE_BALANCE was in documentation but used nowhere
- The used properties are CV_CAP_PROP_WHITE_BALANCE_BLUE_U and CV_CAP_PROP_WHITE_BALANCE_RED_V, however the naming seems dubious

The parameters has nothing to do with the blue or red color channel, rather with the U and V color channel of the LUV color space. They reflect the U and V channel which are used to correct for the current lighting conditions. The scale can be seen here: http://www.codeproject.com/KB/recipes/colorspace1/yuv.png

Removing the dubious names just seems correct now.

Also it seems the interface is supported by dshow, however it only uses CV_CAP_PROP_WHITE_BALANCE_BLUE_U which is strange. I suggest removing that because setting a whitebalance on a single value is not possible...

Currently the CV_CAP_PROP_WHITE_BALANCE_U and CV_CAP_PROP_WHITE_BALANCE_V require an integer value. From manual testing I found the range -0.5 to 0.5 mapped on 0-1000 but I am not sure of this. Should this be mentioned somewhere? Some input please!