Feature/smart scalar bar positioning

• Scalar bars are now draggable and resizeable
• Scalar bars are of reasonable size by default and placed along the 4 edges of the screen by default
• If more than 4 scalar bars have to be displayed, they will appear by default stacked above their parent, in concentric circles. (Scalar bars 1, 2, 3 and 4 appear on Top, Right, Bottom, Left, then scalar bar 5 is stacked under 1 on Top, scalar bar 6 is stacked at the right of scalar bar 2 on the left side, etc.)
• Moving a scalar bar next to an edge automatically rotates the scalar bar to horizontal / vertical
• You can make the scalar bar on bottom appear above the seek bar if there is one by setting a boolean in the Decorator.