Add possiblity to add resources before the sources build phase

[mat1th]

Hello, this is my first contribution to this project. Thanks for your project!

Short description

XcodeGen doesn't support reordering the build phases of a target. This PR adds the possibility to move the "add resources" before the "sources build phase".

Background

As noted in #1042 it is sometimes needed to have the resources already moved before building the app to verify the resources compile time. In the same issue @yonaskolb did note that the way to go is adding a property on target. This PR does implement that.

Implementation

• Added resourcesBeforeSourcesBuildPhase to the Target object
• Check in PBXProjGenerator if the resourcesBeforeSourcesBuildPhase is enabled if so add the PBXResourcesBuildPhase before the PBXSourcesBuildPhase.
• Create and update Unit tests covering this change.

[teameh]

Nice work! Don't forget to:

• Add the property to the docs
• Add an entry to the changelog

[mat1th]

Thanks for the feedback.

I've resolved all issues. Could you recheck the pull request?

[teameh]

\0/ Nice!

[mat1th]

Thank you @yonaskolb for merging!