BackendTemplateView now allows overwriting of template paths to add your own
locations for templates, partials and layouts in a BackendTemplateView based
backend module.

Change-Id: I2d8c4b432ff23a3e9b8b527af4697f31082f64b7
Releases: master
Resolves: #79124
Reviewed-on: https://review.typo3.org/51079


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Mona Muzaffar
Reviewed-by: Mona Muzaffar
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>