Resolves #51 "Add issues notification bubble"

Closes #51 (closed)

Notes:

Adds a red div with a number in it relating to the number of issues currently open for either the Teacher's Teams or the Admin's Teacher's Teams.

Adds a simple REST API for retrieving the information. Added REST is very generic and takes object= queries in the URL to determine what notification numbers to return. Means that the same view is easily expandable if YES or future developers want to add more notification/remaining task number fetching.

Relies on https://stgit.dcs.gla.ac.uk/team-project-h/2021/cs11/ybc-core-fe/-/merge_requests/18

Demo:

Screen_Recording_2022-02-24_at_15.09.30

Manual testing TBC:

• Make sure that the bubble appears on Teacher accounts and displays the correct number of open issues
• Make sure that the bubble appears on Admin accounts and displays the correct number of open issues
• Make sure that number updates after refreshing/navigating after un-blacklisting an issue