Add a 'custom' default app that allows for a completely custom icon and URL

[joeowenca]

At the top of the default apps list/app library, there should be a 'custom app' option. It could use the exact same icon as the 'add app' button that opens the modal.

This custom app option would allow you to add your own Icon URL for a hosted image. As well, a custom URL.

In order to do this, the Next/Image component needs to support custom URLs, in that the width and height props are passed in individually.