Retrieve a saved state of a degree plan

[joalen]

Like the functionality for saving the state of a degree plan, we'd like to also retrieve back the degree plan. Currently, if you try to go to the planner page across different browsers, you'll be back on the same "onboarding screen" like you'd normally be.

We can add onto the logic of going to the planner page automatically, except rather than relying on localStorage first, we can also rely on our backend to retrieve the plan.

In other words, check localStorage first. If not there, then add another check to see if we have it in the backend. If it's in the backend, then, like the localStorage version, we'd just redirect them to the planner stage with the retrieved backend plan stored into localStorage this time. If both are false, then, we can do the onboarding process again.

My goal for this is to be able to improve on the UX experience for the planner page session. If that functionality works, erm, see what we can do about retrieving just the changes made ONTO the degree plan. Like the idea I gave in #99, a similar idea can be done for the retrieval stage.

Acceptance Criteria:

1. Be able to add onto the functionality of retrieving from backend if localStorage doesn't contain their evaluation and be able to save that retrieved plan into localStorage for better caching.
2. If many degree plans, we'd like to "collate" them into "versions" that contains modifications made to their initial plan (see Save the state of a degree plan #99 for more info).