Add automatic index rebuild

[vkbo]

Summary:

This PR adds an automatic rebuild of the project index if not all files in the project's content folder are present in the index when the index is opened. The list of files is registered in the project class when the scan is performed.

Related Issue(s):

Resolves #957

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