Remove white space from Knob.setHintText calls

All knobs were called using 
```c++
knb->setHintText( tr( "Value:" ) + " ", "" );
```
have changed to 
```c++
knb->setHintText( tr( "Value:" ), "" );
```
as the " " was not being used.

If it is felt the + " " is needed i feel it would be better placed in Knob.h

```c++
inline void setHintText( const QString & _txt_before,
						const QString & _txt_after )
	{
		setDescription( _txt_before );
		setUnit( _txt_after );
	}
```