Xcode: Configure more warnings to be detected

See https://github.com/boredzo/Warnings-xcconfig
Xcode: TODO & FIXME comments as warnings
Xcode: Setup tests target for project (XCTest)
Xcode: TODO & FIXME comments as warnings for the tests target
Xcode: Migrate images into an Asset Catalog
Xcode: Reorganise "Model" into "Components"
Xcode: Reorganise view controllers into "Controllers" group/folder
Xcode: Hide storyboard views in a "Storyboards" group
Xcode: Reorganise xcconfig to include code coverage settings