Create pull_request_template.md

A comprehensive pull request template based on the following sources:
- https://github.com/appium/appium/blob/master/.github/PULL_REQUEST_TEMPLATE.md
- https://github.com/axolo-co/pull_request_template

.github/pull_request_template.md

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+## Proposed changes
+
+Describe the big picture of your changes here to communicate to the maintainers why we should accept this pull request. If it fixes a bug or resolves a feature request, be sure to link to that issue.
+
+## Impact
+
+If a feature request or enhancement, please make sure to specify quantifiable impact of your changes on performance, accuracy, reliability, ease-of-use etc.
+
+## Types of changes
+
+What types of changes does your code introduce to ABM?
+_Put an `x` in the boxes that apply_
+
+- [ ] Bugfix (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 not work as expected)
+- [ ] Documentation Update (if none of the other choices apply)
+
+## How has this been tested?
+
+Please describe the tests that you ran to verify your changes.
+
+- [ ] Test A
+- [ ] Test B
+
+## Checklist:
+
+- [ ] My code follows the style guidelines of this project
+- [ ] I have performed a self-review of my own code
+- [ ] I have commented my code, particularly in hard-to-understand areas
+- [ ] I have made corresponding changes to the documentation
+- [ ] My changes generate no new warnings
+
+## Further comments
+
+If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...