Issue templates (#3278)

* Added GitHub issue and PR templates.

* Updated templates

* Update ISSUE_TEMPLATE.md

**Charts version** --> **Charts version/Branch/Commit Number:**

.github/ISSUE_TEMPLATE.md

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+> ℹ Please fill out this template when filing an issue.
+> All lines beginning with an ℹ symbol instruct you with what info we expect. You can delete those lines once you've filled in the info.
+>
+> Per our [*CONTRIBUTING guidelines](https://github.com/jjatie/Charts/blob/master/CONTRIBUTING.md), we use GitHub for
+> bugs and feature requests, not general support. Other issues should be opened on Stack Overflow with the tag [`ios-charts`.](https://stackoverflow.com/questions/tagged/ios-charts)
+>
+> Please remove this line and everything above it before submitting.
+
+* [ ] I've read, understood, and done my best to follow the [*CONTRIBUTING guidelines](https://github.com/jjatie/Charts/blob/master/CONTRIBUTING.md).
+
+## What did you do?
+
+ℹ Please replace this with what you did.  
+
+## What did you expect to happen?
+
+ℹ Please replace this with what you expected to happen.  
+
+## What happened instead?
+
+ℹ Please replace this with of what happened instead.  
+
+## Charts Environment
+
+**Charts version/Branch/Commit Number:**
+**Xcode version:**
+**Swift version:**
+**Platform(s) running Charts:**
+**macOS version running Xcode:**
+
+## Demo Project
+
+ℹ Please link to or upload a project we can download that reproduces the issue.

.github/PULL_REQUEST_TEMPLATE.md

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+### Issue Link :link:
+<!-- What issue does this fix? If an issue doesn't exist, remove this section. -->
+
+### Goals :soccer:
+<!-- List the high-level objectives of this pull request. -->
+<!-- Include any relevant context. -->
+
+### Implementation Details :construction:
+<!-- Explain the reasoning behind any architectural changes. -->
+<!-- Highlight any new functionality. -->
+
+### Testing Details :mag:
+<!-- Describe what tests you've added for your changes. -->