Created Issue: Designer: Codegen not triggered in model-first web site projects [1180]

This is similar to [Work Item 1095](https://entityframework.codeplex.com/workitem/1095), except for model-first instead of database-first.

__Steps:__
1. New Web Site Project
2. New Empty ADO.NET Entity Data Model
3. Generate/Update

__Results:__
* DbContext templates are added to the project (as expected)
* Codegen is not triggered -- template output doesn't exist

__Workaround:__
* Manually click __Run Custom Tool__ on .tt files