user/marble: move soname symlinks to -libs
The soname symlinks were being stored in the marble package instead of the marble-libs package. This led to packages like digikam not working out-of-the-box because the soname symlinks for the marble libraries were missing.
Since the default_libs() implementation ignores the symlinks (a bug IMHO), this needs to be manually implemented on a per-package basis. The marble package was relying on default_libs(). This patch implements a custom libs() to copy over the libraries and their soname symlinks.