removed nonexisting folders from classpath
[xtend] Do go to declaration on F3. Streamlined hyperlinking hovers. (see https://bugs.eclipse.org/bugs/show_bug.cgi?id=443875)

I added 'Open Declaration - ...' to the go to declaration hovers again, as it was quite confusing in some cases to just see the regular label of the referenced element. So now it is always clear that it is the declaration hyper link, but also shows the additional resolved information (i.e. types)

Change-Id: I3aff4867f3e9cee3ac7f1e12360f3592f50d86ad
[xtend][validation] Fix: ConstantConditionsInterpreter uses wrong instance of resolved types 

https://bugs.eclipse.org/bugs/show_bug.cgi?id=450834

Change-Id: I16b6cb80c22936db2ea5980bd818cfd873bad75a
[xtend] @Data avoid NPE (see https://bugs.eclipse.org/bugs/show_bug.cgi?id=451295)
Merge "[xtend][validation] Fix: ConstantConditionsInterpreter uses wrong instance of resolved types "
Merge "[xtend] Do go to declaration on F3. Streamlined hyperlinking hovers. (see https://bugs.eclipse.org/bugs/show_bug.cgi?id=443875)"
Merge "[xtend] @Data avoid NPE (see https://bugs.eclipse.org/bugs/show_bug.cgi?id=451295)"