Same pattern as for evrythng.js, as opposed to current way that creates a global value.

Changes:

• Add separate 'node-style' build output, allowing import ScanThng from 'scanthng'; instead of <script>
• Existing use of <script> should still work. (TODO: test this)
• Don't use window to access evrythng and jsQR
• Require evrythng and jqQR explicitly, allowing use of User scope.

Problems:

• Bundle size increases from 13K to 183K-333K depending on import method due to including evrythng and jsQR directly.
• evrythng.settings inside scanthng.js is not affected by evrythng.setup() called in the implementing app...