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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