Swift Code Integration and Option

[jhb563]

The owa gen command should accept a new option --swift. When run with the swift option, Swift code should be generated instead of Objective C code. When run without this option, Objective C code should be generated.

In order to do this, OWALib.hs will need to be refactored to hook into the Swift generation and printing methods resulting from the appropriate tickets (Issues 73-77).

Note there should be no change in behavior for generating the Localizable.string file. While we call the module OWAStringsObjc, the generated code works perfectly well with Swift code as well.

Additionally, regarding #66, we should track both the latest code generation time for Objective C and Swift. When the user requests Swift code be generated, the generation should happen, even if the relevant files have not been updated since the last Objective C code generation, and vice versa.