Various additions.

- First, modified the ScalebarLayer so that it can be vertically
  centered. Thus, added logic to check if the position is either North
  or South to vertically center the scalebar either at the top or bottom
  of the window respectively.
- Added a removeGeographicTexts method to allow for bulk removal of
  text-objects from the text-layer.
- Refactored the AreaMeasurer and LengthMeasurer to accept parameters of
  type List instead of ArrayList. This cleans up the interfaces so that
  they can be used in more scenarios (for example passing in a
  linked-list as parameter).
- Modified the measuretool to internally make use of a GlobeAnnotation
  instead of using a ScreenAnnotation and manually calculating the
  position every time the annotation changes.
- Added an additional field to the MeasureToolController that sets
  whether the information-annotation is sticky or not. A sticky
  annotation will not dissapear when the mouse-cursor moves away from a
  control-point. Thus, the annotation will cling to the last position
  where a mouse-hover occurred.
- Lastly, added a new class called TerrainProfileAdapter to allow a
  TerrainProfileLayer to be updated from the MeasurementTool. When a new
  control-point is added or an existing control-point is moved, the
  adapter will forward the list of points to the TerrainProfileLayer so
  that the height-profile is displayed in the on-screen window.