Add localization calls to the subnets and the trenda pages.

There are other changes to the common layouts based on simple testing.
Use proper syntax for step 2 title, comment by Joseph Magen
Load the apipie documentation when calling '/api'

The documentation is used to list the links for the resources. We make
sure it's loaded.
Refactoring of Host STI to allow plugins to render a different
STI-type edit form and save the changed type. Also allows the
/fact_values upload to specify a type. Adds tests for the STI type
changes.