SiriusConfig.getProp default to call by name

We don't need to evaluate the default value parameter until it's needed.
This saves a little work and headache, particularly with defaults like
SiriusConfiguration.HOST, where we're using
InetAddress.getLocalHost.getHostName (which is wonky at the best of
times).
Small cleanup of SiriusFactory

Pull out the common prefix in defense of typos. Add a little whitespace
to make it more clear what's going on.
Merge pull request #66 from clinedome-work/getprop-default-by-name

SiriusConfig getProp default => call by name