Properly implementing the MPL (at the file level)

[mattxwang]

note: IANAL

Continuing the conversation in #198, we should properly "implement" the MPL and specify where it doesn't apply. This means adding the file-level header to the relevant files. In particular, it should apply:

• (likely) to the code content of all of our JS/JSX files
• (likely) to the code content of all of our CSS/SCSS files

Importantly, it does not apply to:

• our assets (which aren't really code, per se, and whether or not they're covered under the license can be dubious)
• our data / workshop content (the former is debatable on how we frame it as content, and the latter is typically licensed in its own repository)
• our docs & written content - we can either CC-BY this, or choose to keep it not opensource; open to suggestions

I'm still am amateur in this field, so open to suggestions on how we approach this! Afterwards, might be good to write down the lessons we've learned and/or explain this somewhere in the repo.