Use shared scheme for application target

[n8chur]

Changes

• Moves the Sila.xcscheme from xcuserdata to a shared scheme
• Adds xcuserdata/ to the .gitignore

Overview

These changes making working with the repo as a contributor a bit easier.

The Sila.xcscheme is currently defined in adam.xcuserdatad and adding it to the shared schemes list makes it accessible for other users.

Git ignoring xcuserdata/ means that when another contributor opens the project it will not create a diff which includes user-specific project settings. Adding this to a the .gitignore for a repo that contains an Xcode project is typical (see GitHub/gitignore/Swift.gitignore).

[agg23]

Thanks. I've been out of the Apple dev world for quite a while, so I'm not up to date with current best practices.