Renamed clawutil.clawdata to clawutil.data

This affects many other repositories that will have related pull requests, including 
amrclaw
geoclaw
visclaw
classic (to be done by @gradylemoine)
apps (@mandli needs to update and test some apps)

Main changes needed are in setrun.py, changing to
    from clawpack.clawutil import data
and then set rundata using data rather than clawdata.