Extract Logger Categories to a separate interface

If the logger names could be extracted to constants in an interface,
then it will be easier to make changes to logger names and will also
lead to lesser errors , because logger names are case sensitive

So for example, instead of obtaining a logger like

public static final Logger logger =
Logger.getInstance("OpenEJB.startup",
Assembler.class.getPackage().getName());

We could do something like

public static final Logger logger =
Logger.getInstance(LogCategory.OPENEJB_STARTUP,
Assembler.class.getPackage().getName());

In fact, with static import it will just be

public static final Logger logger =
Logger.getInstance(OPENEJB_STARTUP,
Assembler.class.getPackage().getName());

LogCategory would contain the names of all loggers used in openejb.
Since there are just a few loggers, they could be defined within the
Logger class itself.