Update developer guide 'Implementation' section

[uniqly]

Update the Implementation section:

For any notable feature, include:

• Brief description about the feature (ie: 'About this feature')
• Describe the implementation of the feature
  • Include a Sequence Diagram or Activity Diagram (or both) [REQUIRED for the individual component]
  • Include other diagrams if necessary (ie: Object Diagrams)
• If possible, state design considerations

Refer to past year groups or to the proposed features that already exist for reference.

Create a new Issue for the adding of specific features to the developer guide instead of linking to this issue.

[uniqly]

If you are creating a PR for any feature, including screenshots of the PUML files in the PR would be helpful for reviewers.