Fixed Scene Selector error
Fixed clipping artifacts in parallel projection mode
Shortened skymapFileName setting to skymap

The name change is backward compatible. The "skymapFileName" option is used
if "skymap" is empty.
Updated commandline help output
Fixed snapshot saving errors

- snapshots are now always saved when the SPP target is hit
- fixed overriding of the `saveSnapshots` option in scene configurations

fixes #206 (github)