Add licence text and basic CI (pycodestyle and eslint)

This merge request adds:

• LHCb licence text to each file
• CI check that the LHCb licence text is present
• pycodestyle linting Python
• eslint linting for javascript
• Fixes missing semicolons that were found by eslint

I haven't investigated how best to configure eslint but I think this is a reasonable start.

EDIT: I've just noticed !44 (merged), I guess it would be better for me to rebase this on that PR