Added licenses conversion for NPM packages

[hiqsol]

Thanks to @Roygoldman it turned out that older NPM repositories may have used objects when defining licences.

Please see more detailed explanation at hiqdev/asset-packagist#87

And example of package.json with such licenses:

https://github.com/geraintluff/tv4/blob/master/package.json#L24-L33

[richgerdes]

Thanks, @hiqsol for opening this! It will help my project greatly.

Is there anything that I can do to help move this along?

[francoispluchino]

@hiqsol Thank you!