Remove ':' from imglib2 feature bundle

Feature dependent plugins could not be resolved by eclipse from the
update site because they were not named like the maven bundles. The
solution is to provide an additional plugin-id which is named like the
resulting eclipse plugin (generated by p2-maven-plugin). There is no way
to determin in the script itself what those plugins will be named (it
seems like, they are named by the provided package which cannot be
determined at script-runtime without connecting to maven central
either.)