Selection versus highlighting

Selection and highlighting are visual clues to identify and prepare nobs for a command to be applied to them.

Simple rule:
 * Highlight - Single nob
 * Selection - Multiple nobs

In detail:
 * Only one nob can be highlighted at a time. A selection always includes several Nobs.
 * Highlighting happens automatically as soon as the mouse cursor is over a knob. Selection has to be explicitely caused by the user.
 * The highlighting of a nob automatically disappears if the mouse cursor is no longer over the knob. A selection stays active until the user explicitely stops it with a Deselect command.
 * Selections are visualized by orange interiors. Highlighted nobs have light green edges.
 * When a selection is active, no highlighting happens. All applicable commands (e.g. Copy or Delete) affect the whole selection, not only individual nobs.