Add "Template groups", so templates could be stored there, not in host groups

We have a higher-hierarchy thing called template and lower-hierarchy thing called host. Hosts are attached to templates - this is perfectly logical.

But currently both hosts and templates are "stored" in host groups. This kinda breaks the logic - objects of different hierarchy are stored in same place.
New users wonder why this is so, try to add a template to hostgroup and expect that the template will be attached to every host in that group...

A better solution would be two separate things:

• Host groups
• Template groups.