Add contributing, issue_template and pull_request_template

Author: OskarPersson

.github/CONTRIBUTING.md

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+# Contributing to ESSArch Tools Archive (ETA)
+
+### Did you find a bug?
+
+* Make sure that the bug hasn't already been reported in [ETA](https://github.com/ESSolutions/ESSArch_Tools_Archive/issues) or [ESSArch Core](https://github.com/ESSolutions/ESSArch_Core/issues).
+
+* If no issue describing the same problem exists, [open a new one](https://github.com/ESSolutions/ESSArch_Tools_Archive/issues/new) with as much information as possible:
+    * A title along with a description that explains the problem as clear as possible
+    * A code sample or test case demonstrating the unexpected behavior
+
+### Do you have a new feature or a fix for a bug?
+
+* [Open a new GitHub pull request](https://github.com/ESSolutions/ESSArch_Tools_Archive/compare) with the update
+
+* Reference any applicable issues

.github/ISSUE_TEMPLATE.md

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+*Before submitting this issue, please review our [contributing guidelines](https://github.com/ESSolutions/ESSArch_Tools_Archive/blob/master/.github/CONTRIBUTING.md)*
+
+## Steps to reproduce and/or test case demonstrating the problem
+
+## Expected behavior
+
+## Actual behavior

.github/PULL_REQUEST_TEMPLATE.md

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+*Before submitting this pull request, please review our [contributing guidelines](https://github.com/ESSolutions/ESSArch_Tools_Archive/blob/master/.github/CONTRIBUTING.md)*
+
+## Description
+
+Please describe your pull request.
+
+*Patches should be made against master.*
+
+*If it fixes a bug or resolves a feature request,
+be sure to link to that issue, eg. "fixes #6789".*