Easily install blockpy server's dependencies

[acbart]

We should add a new make command that automatically grabs:

• blockpy.js and blockpy.css from the BlockPy client repo
• block_mirror.js and block_mirror.css from the BlockMirror repo
• skulpt.js and skulpt-stdlib.js from the Blockpy-edu/Skulpt repo
• pygameskulpt.js from the Blockpy-edu/PygameSkulpt repo
• skulpt-pedal.js from the Pedal repo
• skulpt-curriculum-ctvt.js from the Pedal/CTVT curriculum repo
• skulpt-curriculum-sneks.js from the Pedal/Sneks curriculum repo
• Blockly's stuff from the Blockpy-edu/Blockly repo

I assume it's just a matter of getting the right snippet to download and place the file in the right folder: https://gist.github.com/steinwaywhw/a4cd19cda655b8249d908261a62687f8

We'll need to start actually making managed releases with all these projects, but that should be happening anyway.

[acbart]

This should go towards #12 hopefully, since then there are no more hellish dependency chains.