Get the config module working as intended
Use config to locate plugin directories

Rather than hard-coding the path to the '#{ALEMBIC_ROOT}/plugins'
directory in the PluginLoader module, we're now reading a list of
plugin directories straight from the config and loading plugins
from each in turn.
Read hostname and port from config

The 'host' and 'port' settings in the config file are now
respected by the TCPServer module.