Use package names instead of group names

The special comps.xml in silvereye isn't really useful, and the
official Eucalyptus comps.xml does not have groups for anything except
the CLC.  Go back to using package names until we have official groups.
Keep packages in original repos on ISO

The ISO build process originally relied on making a single
dependency-closed repository with packages from several sources.  It
is more acceptable to upstream (CentOS) to keep them separate.  These
changes also allow installation using only updates.img, with no ISO
at all.
Remove patched kickstart.py

The standard silvereye install no longer operates through kickstart,
so we do not need to alter kickstart.py.  Note that the silvereye
install classes do _not_ support kickstarts yet, though.
Fix nfsiso install method
Minor bugfixes; addition of --no-iso build option
Allow for generic CentOS install, using original network screen
Fix HD/USB installs
Fix front end config screen icon
Prune deps for iso-less build
Add startup registration script