Link validation

[rowanc1]

Currently our URLs are too restrictive. This should likely stop with a regexp approach and use a new URL() and look at the throw instead.

For example, doesn't like local hosts with ports, or curve.space. :(

• there is different validation behaviour between the CMD+k initial entry and the validation in the popover

discussion & requirements: https://curvenote.com/@curvenote/architecture/links-in-editor

[stevejpurves]

possibly related: https://github.com/curvenote/editor/issues/139 & https://github.com/curvenote/editor/issues/137

[rowanc1]

Fixed in #142.