Use new version of issue templates (buefy#1545)

This PR also add template for Feature Request and for PR

https://help.github.com/articles/about-issue-and-pull-request-templates

.github/ISSUE_TEMPLATE/BUG_REPORT.md

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+---
+name: Bug report
+about: Create a report to help us improve Buefy
+labels: bug
+---
+
+<!-- PLEASE READ THE FOLLOWING INSTRUCTIONS -->
+
+<!--
+- Try to search for your issue, it may have already been answered or even fixed in the development version.
+- Check if the issue is reproducible with the latest stable version of Buefy.
+- It is **required** that you clearly describe the steps necessary to reproduce the issue.
+- It is recommended that you make a screenshots/animated GIFs/JSFiddle/JSBin/Codepen to demonstrate your issue.
+- If your issue is resolved but still open, don’t hesitate to close it. In case you found a solution by yourself, it could be helpful to explain how you fixed it.
+- Use English for communication
+-->
+
+### Overview of the problem
+
+**Buefy** version: [X.X.X]
+**Vuejs** version: [X.X.X]
+**OS/Browser**:
+
+### Description
+
+<!--Description of the bug-->
+
+### Steps to reproduce
+
+<!--
+1. First Step
+2. Second Step
+3. and so on...
+-->
+
+### Expected behavior
+
+<!--What you expected to happen-->
+
+### Actual behavior
+
+<!--What actually happened-->

.github/ISSUE_TEMPLATE/FEATURE_REQUEST.md

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+---
+name: Feature request
+about: Suggest an idea to improve Buefy
+labels: feature request
+---
+
+<!-- PLEASE READ THE FOLLOWING INSTRUCTIONS -->
+
+<!--
+- It is recommended that you provide screenshots or code samples to demonstrate your issue.
+- Use English for communication
+-->
+
+### Description
+
+<!--Description of the feature-->
+
+### Why Buefy need this feature
+
+<!--Explain why Buefy needs it-->

.github/PULL_REQUEST_TEMPLATE.md

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+<!-- Thank you for helping Buefy! -->
+
+Fixes #
+<!-- If this PR fixes GitHub issue 1234, add "Fixes #1234" to the next line. -->
+
+## Proposed Changes
+
+-
+-
+-