* Beginning to work on image advanced setting type

* Making the maxSize code and UI more user-friendly (hopefully).

* Getting rid of that border, I was using the wrong class

* Displaying an image for the preview

* Not displaying the image if we don't have a value

* Removing no longer used code

* Adding explicit throw in the subscription to make our intents more clear

* Changing some of the Observable style based on  input from the peer review

* Using the maxSizeKB option to enforce the size

* Adding support for no max

* Throwing better errors

* No longer duplicated the multiple usage error message

* Using the maxSize attribute to control the max size of the settings

* No longer using JSON.stringify, it's already a string and that approach
won't really do anything for other data-types

* Extracting validate to it's own method

* No longer hardcoding the maxLength validation in the uiSettings

* Using a Joi schema instead

* Punting on server-side validation for the time being