Introducing ShellBox UI plugin

ShellBox UI plugin - provides SSH connection to a host using
shellinabox - a Web based AJAX terminal emulator
(http://code.google.com/p/shellinabox/)

UI additions:
* Hosts main-tab -> new 'Shell Box' action button
* Hosts main-tab -> new 'Shell Box' sub-tab

Change-Id: I96c234e095e12b276ea6811274e17751de1f0b88
Signed-off-by: Daniel Erez <derez@redhat.com>