Also extract the "supportedBrowser" logic into a helper (rule of 3)

This reverts commit 29d5619d.

* Updates to preview modal for release

* Design tweaks and remove import modal

* Resolve issues with tests

* Copy edits HT Eric

* Resolve lint issue with integration test

* One more change to the disclaimer language

* Add line break

Added:
- Opera (including Opera Mini)
- Silk

Not Added:
- Vivialdi - appears to be ‘Chrome’ in `platform.name`

Initial SB2 Import UI (button in preview modal + import modal that can load projects via url). Preliminary validation on url, still needs error handling.

- implements welcome to the preview modal, and unsupported browser modal.
- will need assets updated in Jan.