Implementers is Broken for Class Files

[tsmaeder]

Search for implementers is broken in jdt.ls branch:

1. Open Runnable.class
2. Put the cursor in the class name
3. Select "Assistant->Implementations" menu
4. Observe: no results.

[tsmaeder]

A cursory inspection reveals that the uri cannot be correctly parsed in org.eclipse.che.jdt.ls.extension.core.internal.navigation.FindImplementersHandler: the field "authority" is null, where it should parse to "contents"