added css grid and converted most pages to use that grid

fixes #660 - getting 404 while refreshing the operating systems selection

adding missing files refs #646

fixes #646 - Creating a host and getting an error results in Operating System not being accepted

Fixes #631 - Adds the ability to set default values for hostgroups, which
are automatically applied when creating a new host (and selecting that
host group), and allows for templates to be rendered with those default
hostgroup values