Draft: switch to generic "path" lookup

$CLARA_PLUGINS required a particular subdirectory structure. Here we switch to $CLARA_PLUGIN_PATH and treat it like a colon-separated list of directories and add a "*" to each for Java's $CLASSPATH type variables. This would, for example, remove the idea of other things being installed inside $CLARA_HOME and any assumptions in CLARA about coatjava/grapes installation structures.

Note, this same or similar functionality also exists in the clara-monitor and clara-shell scripts, so they'll need changing too ...