Feature: Support for excluding file paths

[larssont]

Adds support for excluding file paths

Implements a textarea setting excluded_vault_paths which gets loaded before querying any notes. Notes are then only returned from the vaults if their path is not in the excluded_notes set.

In order to support adding multiple exclusion paths, a newline separates each path in the textarea.

Formatted with Black.

Fixes: https://github.com/Garulf/Obsidian-Notes/issues/16