feature request: support for custom package.json when generating assets

[badpenguin]

I'm using F7 with create-react-app so my project has not been generated using the CLI. When generating assets it will not work because is missing framework7 entry in package.json, please print an error and terminate the script, actually the exception is being ignored. After adding manually the missing parameters i don't like that you cannot customize where icons are generated for pwa, it uses "static" or "assets" instead i'm using "public". It would be nice to have an options for that in package.json. Thanks.