Check unknown options in config

[Nashatyrev]

It often hard to debug if the option name has a typo in user config. So it's worth to check the resulting config for unknown options against ethereumj.conf and either throw exception ( == exit) or print a warning

[cupuyc]

Need to consider next scenario.
Other applications which use ethereumJ as library may use own system properties (-Dprop1=value1). In that case those properties will appear into ethereumJ typesafe config library.

Then exiting could be an option only if parsed ethereumj.conf contains invalid entries.