[ci skip] Add issue and pr template

issue_template.md

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+### Description
+
+
+#### Live Demo
+http://jsbin.com/xukike/edit?html,output
+
+#### Steps to Reproduce
+1. …
+2. …
+3. …
+
+#### Expected Results
+
+
+#### Actual Results
+
+
+### Browsers Affected
+- [ ] Chrome
+- [ ] Firefox
+- [ ] Edge
+- [ ] Safari 9
+- [ ] Safari 8
+- [ ] IE 11
+
+### Versions
+- Polymer: vX.X.X (use `Polymer.version`)
+- webcomponents: vX.X.X (use `bower ls` or `npm ls`)

pull_request_template.md

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+### Reference Issue
+Fixes #9999999
+
+### Description