Add support for ignoring files

[alxshine]

Hello hello 👋 😊

This PR implements the feature requested in #32.

The handling of ignoredFiles is very closely modeled on the handling of auditedFiles.

The checkIfAllSiblingFilesAreAudited now checks if the candidate file is either audited or ignored, causing a directory full of ignored files to be seen as audited. This seemed like the simplest way to integrated it into the existing functionality.

In the explorer view, ignored files are indicated in the same color as gitignored files.

[CLAassistant]

All committers have signed the CLA.

[fcasal]

Hi @alxshine,
I haven't yet reviewed this PR because we want to merge a big refactor of the codebase #48 first.
As a high level comment about the PR I think I would like to handle ignored files using a .weauditignore file -- in a way that if you mark a file as ignored, it would be also added to the .weauditignore file. In that file, you could also specify folders or globing behaviour like you can in .gitignore