JBIDE-17318: Early Access discovery
fix images/cert descriptions; add connectors for AngularJS (JBIDE-17278); remove connectors from Core which are now in EA site
add TODOs and update doc on how to build & test
fix angularjs image reference
update doc and create new jbtearlyaccess target-platform definition
tweak doc slightly to better support child folder path conventions
remove VJET from JBT Central as it's now in JBT EA
include org.jboss.tools.arquillian.feature.feature.group instead of feature
when building discovery site's directory.xml, collect both the local and any other discovery plugins in this project, so the resulting directory.xml contains both core and early access plugins in a single site
add JBT upstream site so that EA content can be test-installed (JBT Arquillian depends on JBT Maven); also, touch the backup repo so it's easier to find in /tmp folder