ScriptRunner: remove verbosity API

You can accomplish the same thing with:

    System.setProperty("scijava.log.level:" +
        "imagej.omero.server.ScriptRunner", "debug")

And the verbosity API was broken anyway because it toggled
the global debug level instead of the local one.
ScriptRunner: fix problem when calling getValue()

Using getDeclaredMethod only finds matching methods in that exact class.
We want all matching public methods in compatible types (i.e., including
supertypes), so we need to use getMethod instead.