Add option to change the unit test target name

Added the ability to specify an alternative name for the unit test target, as suggested by #169. The default is still `UnitTests` to match the previous output.

I also fixed an issue where the project configuration was not being passed to the `FileManager`'s `generate` method, because the `CocoapodsSetup` had not been given access to it.

Thanks for the brilliant tool. I'll be using it to setup my iOS projects from now on! :+1: 
this should be `test_target_name`