Add launching of the Edge browser

[mattyclarkson]

Attempts to resolve #61.

I've had a look into this as I'd like to get Polymer/web-components-tester working with Edge. I can find the executable like this:

var windowDirectory = process.env.winDir;
var systemApps = path.json(windowsDirectory, 'SystemApps');
var edgeDirectory = fs.readdirSync(systemApps)
  .filter(function(folder) {
    return folder.startsWith('Microsoft.MicrosoftEdge');
  })
  .map(function(folder) {
    return path.json(systemApps, folder);
  })[0];

However, this is pretty useless and running the executable doesn't do anything as it's a Windows Store application. It seems you load a web page with:

> start microsoft-edge:https://github.com

The following works:

> python -m http.server 8000
> start microsoft-edge:https://localhost:8000

So I just need to figure out what needs to go into the platform/windows.js file.

[daffl]

Thanks and sorry it took so long. Since the tests are only running in CI on Unix systems we can probably fix them later.