Pull in TrueNAS gui/build under nas_source.

We will be modifying the build to pick files from
this directory instead of using the top level build.

Example would be 'build/files/install_sata_dom.sh',
this file will now come from
nas_source/truenas-components/build/files/install_sata_dom.sh.

And so we shall do it for all the other TrueNAS specific
files.