Add bookmarklet option to support all browsers

This will make the inspector work with all browsers, and will allow for easier debugging of the inspector during development.

To run the bookmarklet in dev mode:
- `grunt bookmarklet_server`
- create a bookmark:

```javascript

javascript: (function() { var s = document.createElement('script'); s.src = 'http://localhost:9191/load_inspector.js'; document.body.appendChild(s); }());

````

Clicking on the bookmark opens a new window with the inspector.  Make
sure to unblock the popup.

This can also be used to debug the inspector (in the popup) using the inspector
extension.

Fixes #145, #184 

- [x] Bookmarklet for development mode (need to clone repo)
- [ ] Bookmarklet for production (upload it to s3, which will make it very easy to use)
- [ ] Fix issues with Safari rendering / css
- [ ] Check if there's a security issue due to the use of `*` in `window.postMessage`