Move resource_templates to heat.scaling

This introduces a new package for autoscaling code which is
intended for use outside of the Heat engine, and moves the
resource_templates function into a new module, heat.scaling.template.
The function hasn't been changed at all.

Change-Id: I78c420e7a188f2d14780a03b3ea220b9a5fbe86c
Implements: partial blueprint as-lib
Merge "Move resource_templates to heat.scaling"