`open_issue` action

Basic rundown:
* Create a file containing the body of the issue
* run `open_issue`
* You will be prompted for the repo name, student file, etc.
* You will be prompted for the issue title
* You will be prompted for the issue file
* :palm_tree: 

Multiple issues will require running this multiple times, with multiple issue files, ...

I have verified that this works, but will need some guidance with writing tests.  I'm also soliciting feedback regarding idiomatic Ruby.  Is there a nicer way to [do this](https://github.com/kelleydv/teachers_pet/blob/2fc0e1ecfb60c57b0c97d89efcb14c12e08c4e79/lib/teachers_pet/actions/open_issue.rb#L18-L19)?

To Do:
* Write tests
* ~~implement issue labels~~