Added the Shape interface
Implemented Shape methods in Circle
Fixed missing closing bracket
Implemented Shape methods in Ellipse
Implemented Shape methods in Polygon
Implemented Shape methods in Polyline
Implemented Shape methods in Rectangle
Removed unnecessary methods and optimized getCenter() in classes
implementing Shape
Removed a redundant implementation of centroid calculation
Renamed Shape to Shape2D
Removed Shape2D#getCenter()
Removed the unused "center" field
Removed unused imports
Merge pull request #2178 from mrgame64/enchancements

Shape interface