Update issue templates

Author: tobiasdiez

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,9 @@
+---
+name: Feature request
+about: Suggest an idea for this project
+
+---
+
+Please use the GitHub issue tracker only for bug reports and suggestions for improvements.
+Feature requests, questions and general feedback is now handled at http://discourse.jabref.org.
+Thanks!

.github/ISSUE_TEMPLATE/question.md

@@ -0,0 +1,9 @@
+---
+name: Question
+about: Ask a question about JabRef
+
+---
+
+Please use the GitHub issue tracker only for bug reports and suggestions for improvements.
+Feature requests, questions and general feedback is now handled at http://discourse.jabref.org.
+Thanks!

.github/ISSUE_TEMPLATE/suggestion-for-improvement.md

@@ -0,0 +1,20 @@
+---
+name: Suggestion for improvement
+about: Suggest an enhancement
+
+---
+
+<!--
+Please use the GitHub issue tracker only for bug reports and smaller suggestions for improvements.
+Requests for completely new features, questions and general feedback is now handled at http://discourse.jabref.org.
+Thanks!
+-->
+
+**Is your suggestion for improvement 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.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.