Update issue templates (#2304)

* Update issue templates

* Create pull_request_template.md

* Create config.yml

Disable blank issues

* Clarifying required info

* Updated bug report template with more details

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: 'type: bug'
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+
+1. run pjsua app with parameter: `--video --registrar sip:some.sip.registrar ...`
+1. make two video calls to: `sip:abc` and `sip:xyz`1
+1. setup video conference: `vid conf cc ...`
+1. assertion occurs!
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Logs/Screenshots**
+If applicable, add screenshots PJSIP logs with verbosity level 5, packet capture (e.g: using Wireshark), audio/video recording, screenshot, etc.
+
+**Desktop/Smartphone (please complete the following information):**
+
+- OS, Distribution & Version: [e.g. MacOS Mojave, Ubuntu 16.04, iOS 13]
+- PJSIP
+  - version: ...
+  - applied patch(es): [e.g: patches from issue/PR xyz]
+  - `configure` script params: ...
+  - `config_site.h` contents: ...
+  - related third party libraries & versions: [e.g: OpenSSL 1.1.1b]
+
+**Smartphone (please also complete the following information):**
+
+- Device: [e.g. iPhone 6]
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/config.yml

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+blank_issues_enabled: false
+contact_links:
+  - name: PJSIP tag on Stack Overflow
+    url: https://stackoverflow.com/questions/tagged/pjsip

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: 'type: enhancement'
+assignees: ''
+
+---
+
+**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/PULL_REQUEST_TEMPLATE/pull_request_template.md

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+<!--- Provide a general summary of your changes in the Title above -->
+
+## Description
+<!--- Describe your changes in detail -->
+
+## Motivation and Context
+<!--- Why is this change required? What problem does it solve? -->
+<!--- If it fixes an open issue, please link to the issue here. -->
+
+## How Has This Been Tested?
+<!--- Please describe in detail how you tested your changes. -->
+<!--- Include details of your testing environment, and the tests you ran to -->
+<!--- see how your change affects other areas of the code, etc. -->
+
+## Screenshots (if appropriate):
+
+## Types of changes
+<!--- What types of changes does your code introduce? Put an `x` in all the boxes that apply: -->
+- [ ] Bug fix (non-breaking change which fixes an issue)
+- [ ] New feature (non-breaking change which adds functionality)
+- [ ] Breaking change (fix or feature that would cause existing functionality to change)
+
+## Checklist:
+<!--- Go over all the following points, and put an `x` in all the boxes that apply. -->
+<!--- If you're unsure about any of these, don't hesitate to ask. We're here to help! -->
+- [ ] My code follows the code style of this project.
+- [ ] My change requires a change to the documentation.
+- [ ] I have updated the documentation accordingly.
+- [ ] I have read the **CONTRIBUTING** document.
+- [ ] I have added tests to cover my changes.
+- [ ] All new and existing tests passed.