Implement ISpellChecker backend for Windows >= 8
Summary:
Provide ISpellChecker backend for Sonnet on Windows
This avoids to ship all the hunspell dictionaries for Windows.
Reviewers: Frameworks, vonreth
Reviewed By: vonreth
Subscribers: mludwig, kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D25244