Redefined basic frame connectors according to that of Multibody in Modelica standard library. Especially:
(1) frame_a has darker blau color compared to frame_b; (2) preserveAspectRatio and initialScale=0.16 introduced;  (3) Introduced 'Diagram' section;  (4) Accordingly, PlanarMechanics.Interfaces.PartialTwoFlanges and a couple of other classes were modified