+ The PGF service now reads and caches dependency label configuration files.
+ The grammar info returned by command=grammar has a new boolean field
'hasDependencyLabels' to indicate if dependency labels were found for
the grammar. Also, command=deptree will now fail if no labels are present.
+ The minibar only shows word dependency trees if labels are present.
+ Also changed the type of getDepLabels from [String] -> Labels to
String -> Labels, since all uses were in the form "getDepLabels . lines".