Create Python Tutor Example in Storybook

[catherinemei]

Created a Python Tutor example, which displays as follows in storybook:

The following files were added under the folder at path: src/python-tutor

• elm-tuple.tsx
• heap-object.tsx
• heap.tsx
• stack-slot.tsx
• global-frame.tsx
• types.tsx

These files contain sub-components of the Python Tutor diagram and are imported in the storybook file (which contains the actual Python Tutor component)

This PR also includes small addition to the Arrow component to control the color of the arrows.

[joshpoll]

Looks good! Could you add an attribution for python tutor? (e.g. link to the website in a comment somewhere) Could you also try to add a circle to the start of each arrow? (The start option on the Arrow component will do this, but I can't tell whether that circle will be centered properly...)

[joshpoll]

I think if you change padStart to 0 it might center correctly?

[catherinemei]

Oh oops yeah I forgot that there's default padding on the arrow. Definitely looks more centered now!