Update the pull request template

[gemmaleigh]

Revert to asking these questions at the point where this project has external contributions.

<!--- Provide a summary of your changes in the Title above -->

## What problem does the pull request solve?
<!--- Why is this change required? -->
<!--- If it fixes an open issue, please link to the issue here. -->

## What does it do?
<!--- Describe your changes -->

## How has this been tested?
<!--- Please describe in detail how you tested your changes. -->
<!--- Include details of your testing environment, and the tests you ran to -->
<!--- see how your change affects other areas of the code, etc. -->

## Screenshots (if appropriate):

## What type of change is it?
<!--- What types of changes does your code introduce? Put an `x` in all the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)

## Put an `x` in all the boxes that apply
<!--- If you're unsure about any of these, don't hesitate to ask. We're here to help! -->
- [ ] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.
- [ ] I have read the **CONTRIBUTING** document.