JBIDE-11099 third PR attempt (fixes indents, removes sourceDirectory=src) >> master

new update site:
* uses packaging=eclipse-repository instead of eclipse-update-site; 
* includes org.jboss.tools.runtime.drools.detector and .feature;
* builds against JBTIS target platform instead of old Helios site; 
* includes index.html page
* has <references> in content.jar that points to upstreamsites to resolve JBT dependencies
* fixes indents (2 spaces, not 4)
* removes sourceDirectory=src