Package USB modules

Add all modules needed for installation on USB storage
Load USB modules

Load USB modules needed to install root on USB flash
Some cleanup
New installer option: rootsize.
Merge pull request #32 from jaketri/master

Fix USB storage access when usbroot is used
Merge pull request #33 from mcanevet/fix/cleanup

Some cleanup
Merge pull request #36 from diederikdehaas/set-domainname

Added option to specify the domainname.
Merge pull request #37 from zimnyx/master

New installer option: rootsize.
Merge branch 'master' of gh:hifi/raspbian-ua-netinst