Vcmatrix colorknob 3

https://sourceforge.net/p/qlcplus/discussion/development/thread/f7238303/?limit=25#a38b

Some changes in VCMatrix:

- Add R/G/B Color knobs to set start/end color of a matrix
- Fix custom controls ordering
- Add checkboxes in vcmatrixproperties to show/hide basic controls
- Fix vcmatrix not receiving any external input if its main slider is not connected to external input
- If 2 VCMatrix are linked to the same RGBMatrix, they will both show the changes we make to the RGBMatrix