Back button rework

[TanyaStere42]

Feature description and context

Now that Scout is being generalized post-KAZA project, we need to allow users to navigate back and forth through the images in a task

Feature sign-off requirements

The changes to the back button should be altered for annotation, review, and ground truth.

• the back button is disabled only on the first image of a task
• the back button is active and available for all other images on a task

Design

on task creation, create an array (or similar structure) that denotes image order. track the position in the array when determining photo to be served