Allow in Incognito mode

[paullewisn]

There does not appear to be a setting to allow this extension in incognito mode:

Other cookie manager extensions have this setting present:

[null93]

This is because I intentionally did not allow this. You can that in the manifest file: https://github.com/null93/milk-cookie-manager/blob/master/static/manifest.json#L12. I will test this extension's compatibility with incognito and enable it if needed.