Adding support for 'Asset Name'.

Content items now have a property 'Asset Name': the name given to the output/copied file.
Importing a contentproj will now import the 'Asset Name' of content items.
Syntax changed from "/build sourcefile" to "/build sourcefile;assetName". /copy changed in same way.
/copy items now get cleaned like regular items.
/copy items now get logged to build output like regular items.
Number of skipped items is now logged alongside success/fail counts.
/launchdebugger option will now break as soon as the option is set rather than after parsing the entire file.