Add 'Open Containing Folder' to Project plugin's tree context menu

Summary:
Plus:

• Reorder Qt include statements alphabetically
• Compact code which adds menu actions
• Make action handling code a bit more resilient by using const
• Cleanup: Remove KIO_VERSION check because it is no longer needed

Screenshot:

Reviewers: Kate, cullmann

Reviewed By: Kate, cullmann

Subscribers: cullmann, broulik, kwrite-devel

Tags: Kate

Differential Revision: https://phabricator.kde.org/D16822