Move Lorax templates into templates.d and a subpackage

https://github.com/rhinstaller/lorax/pull/86 is a patchset to,
hopefully, make it easier for products to customize the boot.iso they
want to create.

It moves the templates from /usr/share/lorax/ into
/usr/share/lorax/templates.d/99-generic/ so that other templates can be
installed without conflict.

It picks the first template directory in templates.d (sorted
alphabetically) or falls back to the old /usr/share/lorax/ path.

--sharedir overrides this and points it to the template directory to
use.

This would allow products, like server, to ship lorax templates as part
of the productimg package and use them during the build process.

Note that the lorax.rst docs haven't been updated yet, and I just
noticed that I need to add a Requires: lorax-templates to the lorax
package to make sure it pulls in something.

Any thoughts on this would be appreciated, either here or in the PR.

Thanks,

-- 
Brian C. Lane | Anaconda Team | IRC: bcl #anaconda | Port Orchard, WA (PST8PDT)