Add caching to PR creation

[richardgaunt]

When we create a PR, it would be great if PR maker saved a progress cache so if the process crashes (like branch not pushed to remote or unpushed changes) then the questions answered and the data that has been entered is retained for next time.

1. Create an in-progress cache, this should be a JSON file with keys for each question answered
2. The cache file should be identifiable by directory on system and which branch the PR was being created for
3. When you open ph_gr it checks for a previous cache and asks "Cache found. do you want to load cache or start fresh?"
4. If you load cache, you still are asked each question but the default answer is what you entered last time (for the changes, we do not cache anything this is just for title and ticket number)
5. When the PR is created, the cache is deleted.