Make updating the base url optional

[stianste]

At the moment when running the generator, the base url will automatically be replaced with whatever host the api was generated against. In our current project we want to keep the base url empty, so that the requests will hit the different environments respectively, e.g (www.test.example.com, www.stage.example.com and www.example.com) based on the contexts it's being called in. This means we have to manually set BASE back to '' each time we run the generator, which is an inconvenience.

It would be great if there was a flag for this, e.g --update-base-url=false or something similar which would allow for keeping the base url unchanged.