Unified GitHub templates accross all projects

Author: Thomas Boerger

.github/ISSUE_TEMPLATE.md

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+1. Please speak English, this is the language everybody of us can speak and write.
+2. Please ask questions or config/deploy problems on our Gitter channel: https://gitter.im/go-gitea/gitea
+3. Please take a moment to search that an issue doesn't already exist.
+4. Please give all relevant information below for bug reports, incomplete details will be handled as an invalid report.
+
+**You MUST delete the content above including this line before posting, otherwise your pull request will be invalid.**
+
+- Gitea version (or commit ref):
+- Git version:
+- Operating system:
+- Database (use `[x]`):
+  - [ ] PostgreSQL
+  - [ ] MySQL
+  - [ ] SQLite
+- Log gist:
+
+## Description
+
+...

.github/PULL_REQUEST_TEMPLATE.md

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+Please check the following:
+
+1. Make sure you are targeting the `master` branch, pull requests on release branches are only allowed for bug fixes.
+2. Read contributing guidelines: https://github.com/go-gitea/gitea/blob/master/CONTRIBUTING.md
+3. Describe what your pull request does and which issue you're targeting (if any)
+
+**You MUST delete the content above including this line before posting, otherwise your pull request will be invalid.**