Add GitHub templates (#1850)

* Add GitHub templates

.github/ISSUE_TEMPLATE/bug_report.md

+---
+name: Bug Report
+about: Create a report describing a bug in MIT App Inventor
+labels: 'bug, status: new'
+---
+
+**Describe the bug**
+
+<!--
+Describe the bug in sufficient detail so that we can understand the issue. You should also describe the steps to reproduce the issue (below) so that we ideally can confirm it.
+-->
+
+**Affects**
+
+<!--
+Please check off the part of the system that is affected by the bug.
+-->
+
+- [ ] Designer
+- [ ] Blocks editor
+- [ ] Companion
+- [ ] Compiled apps
+- [ ] Buildserver
+- [ ] Other... (please describe)
+
+**Expected behavior**
+
+<!--
+Please describe what you expected to happen before you encountered the bug.
+-->
+
+**Steps to reproduce**
+
+<!--
+Please describe the steps needed to reproduce the bug. If possible, please include a minimal example project that demonstrates the issue.
+-->

.github/ISSUE_TEMPLATE/feature_request.md

+---
+name: Feature Request
+about: Describe a new feature for MIT App Inventor
+labels: 'feature request, status: new'
+---
+
+**Describe the desired feature**
+
+<!--
+Describe the feature that you'd like to see implemented for App Inventor. More detail is useful as it allows us to better understand the complexity of the task.
+-->
+
+**Give an example of how this feature would be used**
+
+<!--
+How would a teacher or student use this feature?
+-->
+
+**Why doesn't the current App Inventor system address this use case?**
+
+<!--
+Explain why the use case cannot be completed using the features of the current system.
+-->
+
+**Why is this feature beneficial to App Inventor's educational mission?**
+
+<!--
+Because MIT App Inventor is aimed at educational use, we prioritize development of features with an educational benefit. Help us understand how your feature request relates to our mission.
+-->

.github/PULL_REQUEST_TEMPLATE/default.md

+<!--
+Thanks for contributing a pull request to MIT App Inventor. Please answer the following questions to help us review your changes.
+-->
+
+General items:
+
+- [ ] I have updated the relevant documentation files under docs/
+- [ ] My code follows the:
+    - [ ] [Google Java style guide](https://google.github.io/styleguide/javaguide.html) (for .java files)
+    - [ ] [Google JavaScript style guide](https://google.github.io/styleguide/jsguide.html) (for .js files)
+- [ ] `ant tests` passes on my machine
+
+<!--
+This section pertains to changes to the components module that affect the code running on the Android device.
+-->
+
+If your code changes how something works on the device (i.e., it affects the companion):
+
+- [ ] I branched from `ucr`
+- [ ] My pull request has `ucr` as the base
+
+Further, if you've changed the blocks language or another user-facing designer/blocks API (added a SimpleProperty, etc.):
+
+- [ ] I have updated the corresponding version number in YaVersion.java
+- [ ] I have updated the corresponding upgrader in YoungAndroidFormUpgrader.java (components only)
+- [ ] I have updated the corresponding entries in versioning.js
+
+<!--
+This section pertains to changes that affect appengine, blocklyeditor (except changes to block semantics), buildserver, components (but not changes to runtime), and docs.
+-->
+
+For all other changes:
+
+- [ ] I branched from `master`
+- [ ] My pull request has `master` as the base
+
+What does this PR accomplish?
+
+<!--
+Please describe below why the PR is needed, what it adds/fixes, etc.
+--->
+*Description*
+
+<!--
+If this fixes a known issue, please note it here (otherwise, delete)
+-->
+
+Fixes # .
+
+<!--
+If this resolves an enhancement/feature request issue, please note it here (otherwise, delete)
+-->
+
+Resolves # .