Issue #152: Provide template files for GitHub issues and PRs

- Copied templates from Apache UIMA and adapted them to Apache Annotator

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a report to help us improve
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Please complete the following information:**
+ - Version: [e.g. 0.2.0]
+ - Browser: [e.g. Chrome v123, Firefox v113]
+ - OS: [e.g. Windows 11, Ubuntu Linux 23.4, macOS 13]
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/config.yml

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+blank_issues_enabled: false
+contact_links:
+  - name: Apache Annotator Forum/Mailing list
+    url: https://lists.apache.org/list.html?dev@annotator.apache.org
+    about: Community support.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for this project
+---
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.

.github/ISSUE_TEMPLATE/refactoring.md

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+---
+name: Refactoring (for developers)
+about: Refactor the application
+---
+
+**Describe the refactoring action**
+A clear and concise description of what the action is.
+
+**Expected benefit**
+A clear and concise description of what you expect to improve by the refactoring.

.github/PULL_REQUEST_TEMPLATE.md

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+**What's in the PR**
+* ...
+
+**How to test manually**
+* ...
+
+**Automatic testing**
+* [ ] PR adds/updates unit tests
+
+**Documentation**
+* [ ] PR adds/updates documentation
+
+**Organizational**
+- [ ] PR adds/updates dependencies.
+      <sub><sup>Only dependencies under [approved licenses](http://www.apache.org/legal/resolved.html#category-a) are allowed. LICENSE and NOTICE files in the respective modules where dependencies have been added as well as in the project root have been updated.</sup></sub>