take xtext from releases site

Change-Id: I0a23dacb6f6c30518f27c867a159bb3b8b8ec98a
reintroduced xdoc in the TP

Change-Id: Ib43ea6106f34a162fda9ed01be2e97f2abae8c6e
aggregator for Xtext 2.5

Change-Id: I41f6acaf2f0cc08fdb00872670bd3c44c3eff3ca