treeherder RDBS schemas

This branch adds the directory structure for model, sql, and template schemas.  The template schemas are found in treeherder-service/model/sql/template_schema. Each schema references the database engine to be used as the string "{engine}". This needs to be replaced with "InnoDB | TokuDB | ...", or whatever is appropriate for the run environment before the file is executed in the database. This will be done automatically by a custom django manage.py command that will be included in a subsequent branch.