Range element

### Initial implementation of a new element type with the range of a part. ###

The range element has been added to the "Note heads" palette of the master palette and can be added to a score by dragging and dropping it over a clef. This element type is intended as a system-initial element only and it is laid out in this order (from left to right): clef - key sig. - range - time sig.

Through the Inspector is possible to configure the following properties (in addition to standard element properties):

* group and type of note heads
* with or without a connecting line (with custom line width)
* top and bottom note heads in upright, leaning left or leaning right position
* pitch of top and bottom note heads

A button in the Inspector also allows to automatically update the range to the actual range used by the staff in the score portion from the measure containing the element to the next section break or score end (whichever comes first).

The layout of accidentals added to the note heads is somehow simplistic but, I think, appropriate for the kinds of scores where this type of indication is normally used.

(To avoid introducing new properties and reduce the impact on existing code base, a few properties originally designed for use with figured bass have been 'recycled' for range properties. This can be improved if this new element type is actually merged).

For an initial discussion see http://musescore.org/en/node/23283 (where examples of current implementation will be posted soon).