moved classes a bit around to separate unconnected stuff

usus warning "packages with lack of cohesion"
grid walker improvement: don't get trapped so by "evil" patterns

* added two test cases illustrating the possible traps
* improved debugging/tracing output
new configuration includes both machine types now

configuration now has besides the current configuration also a list of
all PrinterSettings and all PrintSettings. In the xml file the
currentConfiguration only references the settings that make up the
current configuration.

* renamed current.xml to reprap.xml
* removed obsolete configuration files from distro folder
* print settings now also has a name
renamed Extruder/Print/PrinterSettings to Setting

also put a wrapper around the extruders list

note to self: never use plural in type names! (at lease if you ever
intend to use more than instance of that type at a time).
extract materials to top level configuration

and rename MaterialSettings to singular
further promotion of materials: decoupled from ...

ExtruderSetting in PrinterSetting, moved to a list in
CurrentConfiguration.