Add more variety to scaling vectors exercise

Vector doesn't always start at 0, 0 and can be scaled by a wider variety of values.
See Sal's comments in https://docs.google.com/a/khanacademy.org/document/d/1o-Ugr-tjw2EXjJRsPX-1LFkmn4LEW6nM6g8l--XGLYU/edit?disco=AAAAAGVQGYA#

Test plan: reload a bunch in local mode and answer questions

Auditors: alpert