Logger: remove custom Logger class, use stock log4php

Our Logger class was a thin wrapper over the stock log4php class, and
was reloading the config file for each class instantiation. Move the
config loading code to the server, and fetch the loggers from the Logger
singleton as required.
Bugfix: supply a proper callable object to propPatch handler

The previous object was not a callable, but the result of a function
call.