Adding the auto updater feature using sparkle

[Mattcbr]

PR Details

This adds a new feature to mockingbird where it will be able to update itself.

Description

• This adds the Sparkle framework to the project. This framework enables the app to auto update, which will improve the project user experience overall.

• Also, makes all the binding necessary to integrate the project with the Sparkle framework

• And finally, it adds the new AppCast file, which will be used in order to make the updates to the next versions possible.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

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