explicit Session.Phase indication with associated event bus;
asynchronous Session.start();
synchronous Session.stop();
added Plugin.session_manager on top of basic Session;
eliminated separate isabelle.activate action;
misc tuning;
<?xml version="1.0"?>
<!DOCTYPE ACTIONS SYSTEM "actions.dtd">
<ACTIONS>
<ACTION NAME="isabelle.session-panel">
<CODE>
wm.addDockableWindow("isabelle-session");
</CODE>
</ACTION>
<ACTION NAME="isabelle.output-panel">
<CODE>
wm.addDockableWindow("isabelle-output");
</CODE>
</ACTION>
<ACTION NAME="isabelle.raw-output-panel">
<CODE>
wm.addDockableWindow("isabelle-raw-output");
</CODE>
</ACTION>
<ACTION NAME="isabelle.protocol-panel">
<CODE>
wm.addDockableWindow("isabelle-protocol");
</CODE>
</ACTION>
</ACTIONS>