Feature : Multiple build configuration support

[shoebox]

• Add support of project with multiple sub target configuration (ex: topshelf)
• cf the TargetConfiguration class for the DSL detail.
• Example of usage:

xcodebuild {
//usual configuration
}

targetConfiguration {
	all {
		// apply to all target configurations
	}

	TestConfig {
		provisioningFile = project.file("path/to/file")
	}

	TestConfig_TopShelf {
		provisioningFile = project.file("path/to/file")
	}
}