[issue #50] added a repaint in equalizer model listener so that the spline (if painted) will be displayed correctly if there is a change that did not origin from the sliders
[issue #50] to string impl for range
[issue #50] proper impl for enabled toggle
[issue #50] Fix bug that causes Rubberband model to become invalid

The RubberBand model of the equalizer panel could become invalid under
certain conditions. A value of -1 could actually occur for a category if
the carryover is negative and the goodIndexes list contains indexes that
point to 0 values. This is the case if the initial delta is smaller than
the number of available indexes (the first and only valueDelta is 0).
The carry over distribution section now handles this case correctly.