Adding Asana integration

This PR builds on the great work by @jurre to add Asana integration to Crashlytics.  There's some clean up here to bring it in line with our (unpublished) style guide, and a small change to ask for the project id directly in the UI rather than the URL.

This PR can be approved and merged now, but the feature of Asana integration has dependencies on PRs for other internal repositories.  Those are ready to go and those will be submitted once this one is approved.

Here's the flow:

**Crashlytics integrations window:**
![step1](https://f.cloud.github.com/assets/1056957/427945/c53f0dfc-adf5-11e2-98f2-67c559baaa55.png)

**Steps for getting API key in Asana:**
![asana_api1](https://f.cloud.github.com/assets/1056957/427963/4572f286-adf6-11e2-804f-df5cfc5b9a8b.png)
![asana_api2](https://f.cloud.github.com/assets/1056957/427966/76f22b92-adf6-11e2-88cd-6baa7cce5e0b.png)


**Grabbing project id:**
![asana_project_id](https://f.cloud.github.com/assets/1056957/427959/343a4c76-adf6-11e2-866e-94e660ad7142.png)


**Task added in Asana:**
![payoff](https://f.cloud.github.com/assets/1056957/427968/83f00e18-adf6-11e2-8451-837fa0307b18.png)

@jurre, let me know if you have any other thoughts and thanks a lot for the PR!  We'll get it in production tomorrow or early next week at the latest.