Fix bugs preventing dSYM upload for development builds by using upload-symbols tool

[andrewhavens]

While trying to figure out why development builds weren't symbolicating correctly, I found the upload-symbols tool that comes with the Fabric CocoaPod. I switched to using that and it was able to symbolicate correctly. Not sure if we want to switch to that for release builds too, but it seemed to work for development builds.

Fixes #11. Fixes #12.

[andrewhavens]

@MarkVillacampa Do you mind reviewing this for me?

[MarkVillacampa]

Hey @andrewhavens! Thanks for taking the time to write this patch.

I believe using the upload-symbols tool is the way to go. The run tool is too tied to the Xcode build process. I think it's safe to use it in release builds too, and we will be able to remove a lot of code in the process :)

The only thing I'm worried about is the rake fabric:setup task. Unless the way to register a new app with Crashlytics has changed, it requires running the run command to register your app. Maybe we can change the setup task so it uses the run command, and let the dsym task use the upload-symbols command.