Optionally specify xcodeproj path for 'frank setup'

Similar to the PR I just sent, I regularly have my xcodeproj files outside the workspace root, which means `frank setup` cannot find them.

I have added a `--project` option to `frank setup` where you can provide the relative path to the xcodeproj file.

In my app:

```
workspace
+ -- want to run `frank setup --project app/app.xcodeproj` from here.
+ app
    + app.xcodeproj
+ Pods
+ other stuff
```

In the case where the --project flag is not specified, it falls back to the existing behaviour.