Fix: Delete Device Models

Also purge related Device Components and any Device Model Image
Fix: Disable HTTP KeepAlive

To improve support for proxy servers which do not support this
optimisation.
See:
http://discoict.com.au/forum/support/2013/2/connection-issues,-lwt,-updates-etc.aspx
Remove obsolete plugin references
Update: Community Plugin Library
Update: Plugin Framework Install & UI