fixes #11175 - [API] Add taxonomies to ptables, display ptables in taxonomies

(cherry picked from commit d1e6d79eb8c469ecf3c66fc15ba5fe8c1333836c)

Fixes #10917 - Update API docs for template combinations

Fixes #6976 - Build default PXE menu should be POST request

Fixes #7096 - Adds STI to templates

This commit converts Ptables to be just another type of Template so it
gets the same features as ConfigTemplate. ConfigTemplate was renamed to
ProvisioningTemplate to reflect UI and the name under it's commonly known.

fixes #10720 - Adds API to get host vm attributes

This exposes an API to fetch a host's vm_compute_attributes,
such as vmware cpus and memory. It lives at a separate endpoint
because it involves a fetch for data from the compute resource,
and may have different performance characteristics than the database.

fixes #9031 - Add routes to view template_combinations per hostgroup / environment

fixes #10167 - change default API from v1 to v2

Refs #3809 - Remove cops for empty lines

fixes #9030 - Adds support to clone config template via api

fixes #7586, #7734, #7172 - user preferences for receiving mail notifications

Adds a framework for user-selectable mail notifications. The work is
still done in ActionMailer classes and launch by rake in cron, however a
wrapper called MailNotification is used to provide RBAC and make the...