improved interface for property and constraint collection
split generic properties from type properties
rename nbl directory
connect nabl-property-eq and property-eq
moved properties related code, use editor/origins instead of clone
moved properties related code to right places
more regrouping
simpler interface
several bug fixes
rename
PropCheck needs to return the matched type, not the actual one
avoid re-collection on leaves
Merge branch 'master' into constraints

Conflicts:
	org.spoofax.meta.runtime.libraries/nabl/tasks.str
nabl-props callback needs to preserve the original term
another fix for prop collection
support for property list task
toward more generic base tasks
check constraints w/ existing tasks
cleanup tasks

- renamed Concat to Combine, since it combines results of other tasks to
the results of a single task
- introduced Collect, which collects the results of other tasks into a
list, the single result of this task
- removed obsolete Match task (can be handled by Rewrite)
more work on clean tasks