--tag option to spin-livecd or spin-appliance

[Jay Greguske]

Hello,

This patch implements a --tag option to the cli for the spin-appliance or spin-livecd
directives. It causes the <target> parameter to be interpreted as a tag rather than
a target. The patch includes minor changes to the client, builder, and some simple logic
in the webUI to keep the task options listing clear to the user.

Thanks,
- Jay