Background Media Plugin: Type Image: Add background repeat feature.

Problem/Motivation

Currently we have no way to set the background repeat option, it is currently hard-coded to no-repeat.

Steps to reproduce

Upload a background image via the media field. Inspect the section with the background attached to it.

Proposed resolution

We want the user to be able to select the way the background will repeat and have it reflected on during the layout building experience.

Remaining tasks

Add a UI element for selecting the way the background repeats.

User interface changes

TBD.

API changes

n/a

Data model changes

n/a