host permissions granting and tab events listening review

We're in trouble with the current way of handling the nuxeo server connection attempts. As a results, we may still send requests to not-allowed servers, such as connect servers. It's difficult to handle and we should find an easier way to proceed.

Instead of listening for all tab events, we may introduce an options page where the user will be able to define which server she wants to interact with.

This way, we will be able to remove the hard-coded host permission for http://localhost:8080/* and let the user choose the one she wants and grant the appropriate host permission at this time.

We could display a page hosted by the web-extension and a context-menu item to access it. I already worked on that subject and the code is available in the branch feature/host-permissions