Update issue templates

Author: keveleigh

.github/ISSUE_TEMPLATE/---bug-report.md

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+---
+name: "\U0001F41B Bug Report"
+about: Create a report to help us improve
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+_(Links to sample GitHub project preferred)_
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Actual behavior**
+A clear and concise description of what happens instead.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Unity Editor Version**
+Which Unity version(s) you've been able to reproduce the bug in.
+
+**Mixed Reality Toolkit Release Version**
+Which MRTK version(s) you've been able to reproduce the bug in.
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/---feature-request.md

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+---
+name: "\U0001F195 Feature Request"
+about: Suggest an idea for this project
+
+---
+
+**Is your feature request 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.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.

.github/ISSUE_TEMPLATE/---vnext-task.md

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+---
+name: "\U0001F4DD vNext Task"
+about: File an outstanding task for vNext.
+
+---
+
+**Overview**
+A clear and concise description of what the outstanding task is.
+
+**Requirements**
+A list of the required features this task will implement.
+* Requirement 1
+* Requirement 2
+
+**Acceptance Criteria**
+A list of the specific things that must be done for approval and acceptance here, done in checklist form. This may correspond with the above requirements.
+- [ ] Criterion 1
+- [ ] Criterion 2