Basic support for PHP and Python fenced code blocks in Markdown

Summary: This patch enables syntax highlighting of PHP and Python code blocks in Markdown code.

Reviewers: Framework: Syntax Highlighting, vkrause

Reviewed By: Framework: Syntax Highlighting, vkrause

Subscribers: cullmann, dhaumann, cfeck, kwrite-devel, Frameworks

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D7864