Re-implement the status and importance flags

[vkbo]

Summary:

This PR completely rewrites the NWStatus class, the class that controls all the status and importance flags in the project.

With this change, the text of the label is no longer the information stored for each item in the project. Matching those with the pre-defined list was always a bit risky due to the way XML treats text. In this new implementation, each status or importance flag is given a key, which is either an "s" or an "i" followed by a random 24 bit value in hex. This decouples the visible label from the underlying flag, which means there is no need to update the values for the project items when a flag is re-labelled. It's the same logic that is used with the item labels themselves.

Related Issue(s):

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All flake8 checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed