Enhanced Navigator Resizability (#280, #296)

No breaking changes.

New ControlAnchor.ABSOLUTE enum for positioning controls anywhere in viewer.

New 'navigator-scroll' event fired by Navigator.

Revised/New navigator options:

* @property {Boolean} [showNavigator=false]
*     Set to true to make the navigator minimap appear.
*
* @property {Boolean} [navigatorId=navigator-GENERATED DATE]
*     The ID of a div to hold the navigator minimap.
*     If an ID is specified, the navigatorPosition, navigatorSizeRatio,
navigatorMaintainSizeRatio, and navigatorTop|Left|Height|Width options
will be ignored.
*     If an ID is not specified, a div element will be generated and
placed on top of the main image.
*
* @property {String} [navigatorPosition='TOP_RIGHT']
*     Valid values are 'TOP_LEFT', 'TOP_RIGHT', 'BOTTOM_LEFT',
'BOTTOM_RIGHT', or 'ABSOLUTE'.<br>
*     If 'ABSOLUTE' is specified, then navigatorTop|Left|Height|Width
determines the size and position of the navigator minimap in the viewer,
and navigatorSizeRatio and navigatorMaintainSizeRatio are ignored.<br>
*     For 'TOP_LEFT', 'TOP_RIGHT', 'BOTTOM_LEFT', and 'BOTTOM_RIGHT',
the navigatorSizeRatio or navigatorHeight|Width values determine the
size of the navigator minimap.
*
* @property {Number} [navigatorSizeRatio=0.2]
*     Ratio of navigator size to viewer size. Ignored if
navigatorHeight|Width are specified.
*
* @property {Boolean} [navigatorMaintainSizeRatio=false]
*     If true, the navigator minimap is resized (using
navigatorSizeRatio) when the viewer size changes.
*
* @property {Number|String} [navigatorTop=null]
*     Specifies the location of the navigator minimap (see
navigatorPosition).
*
* @property {Number|String} [navigatorLeft=null]
*     Specifies the location of the navigator minimap (see
navigatorPosition).
*
* @property {Number|String} [navigatorHeight=null]
*     Specifies the size of the navigator minimap (see
navigatorPosition).
*     If specified, navigatorSizeRatio and navigatorMaintainSizeRatio
are ignored.
*
* @property {Number|String} [navigatorWidth=null]
*     Specifies the size of the navigator minimap (see
navigatorPosition).
*     If specified, navigatorSizeRatio and navigatorMaintainSizeRatio
are ignored.

Fixes #280 and #296