Removing AllTests, as that isn't really needed today anymore.. both IDE
runner as well as Tycho can run simply any tests they find.  More
importantly it initially caused me confusion, because I had tests
showing up double, and strange side effects, when just using the Run All
Tests in Project.
Minor changes from code re. gen. with latest Xtext 2.4.1
Comments only, no actual change (compared it with current 2.4.1 example;
looks fine)
Aligned non-gen. plugin.xml with new plug.xml_gen including changes from
re. gen. with latest Xtext 2.4.1. Manually compared it, all looks about
right..
SerializationTest failed completely with injection problem; with this
now 2 pass, 1 'real' problem (testReferenceTest) TBD.