Title Padding for UIButton

Hi! 

This is my first pull request to Teacup. :smile: Let me tell you that it is an great library. It has help us tremendously because it separates the styles and the programing part. It also help our designer to jump and adjust the project. Thank you very much. 

This pull request is just a handler to allow padding for UIButtons. I am still a bit lost when it comes to test things like this. I would love any guidance on it. :pray: