Overridden add operations for mobjects

[TurkeyBilly]

Motivation

• To make combining mobjects to a Group of mobjects and adding mobjects to a group more convenient.

Proposed changes

• In file mobject.py, added add function and mul dunder function for Mobject, returning a Group type accordingly
• In file vectorized_mobject,py, added add dunder function

Test

Code:

class testscene(Scene):
    def construct(self):
        cir = Circle()
        sq = Square()
        group1 = (cir*6).arrange_in_grid(2, 3)
        print(type(group1))
        self.add(group1)
        group2 = (cir+sq).move_to(DOWN)
        self.add(group2)
        print(type(group2))

Result:

<class 'manimlib.mobject.types.vectorized_mobject.VGroup'>
<class 'manimlib.mobject.types.vectorized_mobject.VGroup'>

[3b1b]

Looks good! Just one minor tweak.