Add tests to any app

Users can view all apps (created by anyone) and their associated tests. However, users can only manage apps that they created. 

Here are some screenshots (***Note: each app belongs to a different user***):

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Users can view all apps and their associated tests:
![image](https://cloud.githubusercontent.com/assets/2835199/2691926/ed4a5a1a-c391-11e3-9c5f-01cc5de6c2d4.png)

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Users can create a new test for any app:
![image](https://cloud.githubusercontent.com/assets/2835199/2691927/f9488cba-c391-11e3-893d-1bda8c34752e.png)

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Users can only manage apps they created:
![image](https://cloud.githubusercontent.com/assets/2835199/2691935/4fa5ed14-c392-11e3-80ba-b8af426eeb37.png)

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