Split opencv stuff to lib and plugin subfolders
Add value_type typedef
Move histogram handles to a separate file

Cleaned up backProject() code at the same time.
Move yuv to rgb conversion to colors module
Clean up docs
Add labeling functions that take output image as input
Make threshold handling consistent

PiiThresholdingOperation and PiiLabelingOperation handled threshold
inversion differently. Fixed.
Add dependency on colors to camera module
Add parentOperation(), dynamic metaproperties

- metaProperty() now converts "false" and "true" to booleans
- Added support for metaproperty getter functions