Introduce data caching in grade service

What does this MR do?

This MR caches the data fetched by the grade service to the session storage. This way whenever an api call is invoked by the grade service, we have the following workflow:

• if the function of the API call was not invoked till then, it proceeds with making the API call, fetches the data and saves it in the session storage.
• if the function of the API call had already been invoked earlier, it just gets the data from the session storage.

By doing that, the user uses less data and there are less API calls to our API server.

Related issues and links

Fix #252 (closed)

Developer Checklist

• I have successfully run the code of this merge request locally

• I have verified locally that my changes work for all necessary screen sizes

• I have tried out the changes of this MR with different users to identify bugs

• Coding is in progress, and I have marked the MR as WIP

• Coding is completed and the MR is ready for review

• My branch is up-to-date with the upstream master branch

• My MR follows the contribution guidelines

• I have added a comment with screenshots of the code running locally

Tech review Checklist

Have you verified that what is supposed to happen, actually does, and what is not supposed to happen, indeed does not?

• The MR accurately describes the changes and has a relevant title/description
• The MR does what it is supposed to according to its title, description and related issues/links
• I have successfully run the changes locally, and tried the new code

Overall review Checklist

• The MR references related issues/MRs
• The MR provides links to screens and screenshots
• The commits of the MR describe the changes, have proper wording, and follow the guidelines
• I have successfully run the changes locally, and tried the new code
• The MR is ready for merge (rebased, commit squashed if needed, etc)

Closes #252 (closed)