Issue 1315

Id's are removed as this components are now being used more than once.
The on enter key action is replaced with a traditional button that becomes active when the user enters both values. The error labels are now redundant.
Better (IMO) to have this component (i.e. the `NCWMSColourScalePanel`) emit an event (say `scaleUpdated`) for which the `StylePanel` listens.

This is better mainly because it decouples this component from `NCWMSColourScalePanel` (making it easier to change things around later).