Repo structure alignment

[Silic0nS0ldier]

To aid maintenance, NPM repos in the UserFrosting project aim for structural and CI parity. As a package which has been transferred, there are differences to reconcile.

• Use AVA for unit testing
• Relocate source to src
• Adjust code style
• Adjust filename casing
• Port package scripts (plus additional checks)
• Bring CI to parity (currently steps are commented out/replaced)
• Migrate source to TypeScript