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:

{F6414525}

Reviewers: #kate, cullmann

Reviewed By: #kate, cullmann

Subscribers: cullmann, broulik, kwrite-devel

Tags: #kate

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