Add extra patch to differ stack that tracks difference between base_state and Neuroglancer initial state

When Neuroglancer loads a base_state for a task, it rearranges the JSON attributes and explicitly adds attributes that were pre-defined implicitly. Example:


This causes a discontinuity between the earliest state that the differ stacks track and the base_state which has been stored in the task metadata. Even though the two states are technically identical, the patch application fails.

The library that Neuroglancer uses to create patches is here -> https://github.com/google/diff-match-patch

For this task, resolve this discontinuity by generating an extra patch at the head of the differ stack which tracks the difference between the base_state and Neuroglancer's earliest recorded state.