Allow DC-files to be Symlinks

[fsundermeyer]

DAPS currently resolves symlinks and assumes that the resulting rean directory is $PROJECT_DIR.
This behaviour is probably unexpected and in case it causes problems, hard to debug.
This also requires to copy DC-files into localization rather than just linking them from the source language.

Target: DAPS 4.0

[fsundermeyer]

A link to a DC file could be anywhere in the file system and there would be no way to automatically determine $PRJ_DIR (the location of the source directories). The only possibility wouid be to always specify BUIDDIR, SRC_DIR, and IMG_SRC_DIR.
Solved this (at least temporarily) by not allowing symbolic links to DC-files with 7ede660

Leaving this open to find a better solution, because the root problem is the automatic detection of directories. If we assume that a DC-file is always located in PRJ_DIR, we should check if this is the case.