Update/enhance base Xcode template

These are just some small modifications to the iOSOpenDev base template. They:
- add an option to fill in the company/organization name so the standard `__MyCompanyName__` can be avoided
- enable ARC by default in new projects. Other than the added convenience, this also fixes some memory leaks introduced in e8d6141f2b504bd6663beaecc9d00ce5f01ac4c1, e.g. in the NC widget template.

(@kokoabim: I'm assuming that the code I'm talking about expects ARC to always be enabled, but for some reason it just wasn't before. With ARC on, everything's fine. :wink:)