Support new import syntax

[jribbink]

Is your feature request related to a problem? Please describe.
The playground does not support new import syntax (i.e. import "FooBar")

Describe the solution you'd like
Implement a resolver similar to address imports for string imports instead. There may be additional UI work necessary to make it clear where these imports are coming from.

Describe alternatives you've considered
n/a

Additional context
Blocked by onflow/cadence-tools#168. Can only be done once the language server is configured to call the JS resolver from the DOM.

[gregsantos]

Needs Language Server updates from onflow/cadence-tools#168