[TASK] Use enumeration for handling conflicts in file names

Conflicts in file names are handled with a list of plain
text values in the code. This patch adds a DuplicationBehavior
enumeration to improve the situation. It also streamlines the
redundant use of different strings for the same thing.

Change-Id: If07cacc77a4737bf52e6978dba79c22d72b7209c
Resolves: #55419
Releases: master
Reviewed-on: http://review.typo3.org/42794


Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Frans Saris <franssaris@gmail.com>