Fix incompatibility with inline Rmodules plugin setup introduced by latest changes

A great way to develop concurrently on transmartApp as well as on Rmodules is to enable Rmodules as an inline plugin rather than pulling it in as a plugin dependency.
This setup was broken by a commit introducing rdc-rmodules in a deprecated way in application.properties. This patch will fix that and re-enable this setup again, while leaving the default at just pulling in rdc-rmodules as a plugin dependency.
(trying to be verbose to support community uptake :-))