Add sources to the JBDS target platform

We are maintaining target platfroms for JBT [1] and for JBDS [2] separatelly. The only difference is that TP for JBT includes sources but TP for JBDS doesn't.

Consequently, JBT users can install plugins including sources but JBDS users can't. In my opinion both should have sources.

[1] http://download.jboss.org/jbosstools/targetplatforms/jbosstoolstarget/4.70.0.AM1-SNAPSHOT/REPO/plugins/

[2] https://devstudio.redhat.com/targetplatforms/jbdevstudiotarget/4.70.0.AM1-SNAPSHOT/REPO/plugins/

If we decide to add sources to JBDS TP, we'd be able to drop one of the TPs entirely and just build one for both JBT and JBDS, saving time and disk.

I will ask people at jbosstools-dev for their opinions.

CC: nickboldt