JBIDE-15156 : add minimal ui deps for tomcat detection

- added org.eclipse.jst.server.tomcat.ui dependency to org.jboss.tools.wtp.runtimes.tomcat/META-INF/MANIFEST.MF, so that no missing icons show up in preferences > servers runtime environments
- added computed plugins from org.eclipse.jst.server_ui.feature to org.jboss.tools.wtp.runtimes.tomcat.feature/feature.xml, so the server view shows up and servers can be actually used (started/stopped). Adding org.eclipse.jst.server_ui.feature to features.xml made tycho ignore the locally built org.jboss.tools.wtp.runtimes.tomcat.feature in the local p2 site, for some reason.
- fixed groupid of org.jboss.tools.wtp.runtimes.tomcat.feature

Signed-off-by: Fred Bricon <fbricon@gmail.com>