Parts.Fixed: According to appropriate models in Modelica standard library (e.g. Modelica.Mechanics.MultiBody.Parts.Fixed), the Fixed block has to introduce frame_b instead of frame_a
Examples: Documentation: Corrected duplicate definition of 'revisions'
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
Merge pull request #49 from tobolar/master

Couple of models adapted to have similar behaviour like appropriate models from Modlica.Mechanics... (e.g. 'Fixed', 'Frame_a', etc.)