add optional parameter to index.html

This update allow passing a json file URL as a parameter to the index.html file.
for example http://localhost:8000/ui/index.html?src=http://localhost:8000/ui/api/api-docs.json

This will not be useful when the GUI is hosted on OSv itself, but will make it easier to use the same html files on github pages, for example.

To use src parameter with a different json host than index.html itself, one need to allow CORS on the server.
If this is not the case, you might get a 
"Can't read from server. It may not have the appropriate access-control-origin settings."

To match proper swagger-ui process, update made on src/main/html/index.html, and built using 
```npm run-script build```