Added some tests for Shape class and Cube class.

To be noted that Cube class is a subclass for Shape class
Also the method .homogeneous_transform() is not in Shape class.
It would be rather implemented in VisualizationFrame class.
Added some tests for the existing test_shape, and test_cube.
Added tests for class Cylinder, which is a subclass of shape.
Added test for cone Shape, initialized a new file for writing tests for
VisualizationFrame.
Added tests for Shapes as per discussed to include attributes, instead of
explicit getter,setter methods
Added tests for MeshShape class
Added tests for Plane class
Modified tests for shapes to include test for class constructors.
Added tests for Torus class
Added tests for Tube class
Added tests for Visualization frame.
constructors using a rframe/point and using rigidbody are incorporated in
the tests
Added tests for all Shapes.
Added tests for shapes
Merge branch 'tests-shapes' of https://github.com/tarzzz/pydy-viz into tests-shapes

Conflicts:
	tests/test_shapes.py
Modified Icosahedron shape tests, removed some errors
Added colors as per the matplotlib's color module.
Colors would be defined as strings of some keywords, or html hex codes,
which would then be converted to rgba vals by using matplotlib's ColorConverter
Added __str__  and __repr__ methods to tests, changed MeshShape to Mesh
Changed ints to floats like, 0 to 0., Ready to be merged
Removed center argument from shapes tests
Added tests for data generation