[TASK] thumbs.php ease require/include path

Currently typo3/thumbs.php requires t3lib/thumbs.php and
t3lib/thumbs.php requires EXT:backend/Classes/View/ThumbnailView.php.

Include ThumbnailView directly in typo3/thumbs.php.
But keeps deprecation in place and other files untouched.

Change-Id: I1c464e683cb08f674ac47cb87f296b185fd35db5
Fixes: #46308
Releases: 6.1
Reviewed-on: https://review.typo3.org/18928
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
[TASK] Update file type according to Iana standard

This change relates to the File types in FAL.
The Iana standard http://www.iana.org/assignments/media-types
defines a list of Media types which are followed in TYPO3 CMS.
It looks the "Software" type should be deprecated and replaced by
"Application". This matches the mime-type e.g application/pdf and
sounds more comprehensive.

Change-Id: Ic2ec7173d10b6139e6e2a19fcead3086665a3aae
Fixes: #45503
Releases: 6.1
Reviewed-on: https://review.typo3.org/18297
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack
[TASK] Small clean up in the page tree code

There are minor issues in the page tree code, which should be
cleaned up. This is a non-functionality change.

Change-Id: Ia4a27797293cb94d58927036ec33dd28a02d0961
Resolves: #46435
Releases: 6.0, 6.1
Reviewed-on: https://review.typo3.org/19049
Reviewed-by: Mattias Nilsson
Tested-by: Mattias Nilsson
Reviewed-by: Wouter Wolters
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack