Add a tool to download spell check dictionaries

[vkbo]

Summary:

This PR adds a dialog/tool to download hunspell dictionaries into the local enchant folder. These will immediately be available as spell check options. This is particularly useful for Windows, where no dictionaries are picked up from the local OS.

Related Issue(s):

Closes #982

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

[vkbo]

Closed in favour of #1611