The roscpp-core package is a meta-package. This meta-package and the concept
meta-package in general is not used for any purpose in our layer.

Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>

removing RDEPENDS because we cannot check if it works as intended, as long as we are just compiling, but not running ROS.

gathering all packages in the meta package roscpp-core in the folder roscpp-core for better structuring

a metapackage is an empty package; switching from RDEPENDS to DEPENDS because it works, but it is not clear if that is really what I intend to express