[ADD] Github template files for issues and PR

.github/ISSUE_TEMPLATE.md

+Impacted versions:
+
+Steps to reproduce:
+
+Current behavior:
+
+Expected behavior:
+
+Video/Screenshot link (optional):
+

.github/PULL_REQUEST_TEMPLATE.md

+Description of the issue/feature this PR addresses:
+
+Current behavior before PR:
+
+Desired behavior after PR is merged:
+
+
+--
+I confirm I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr

CONTRIBUTING.md

@@ -8,7 +8,7 @@ TL;DR
 * If you [make a pull request](https://github.com/odoo/odoo/wiki/Contributing#making-pull-requests),
   do not create an issue! Use the PR description for that
 * Issues are handled with a much lower priority than pull requests
-* Use this [template](https://github.com/odoo/odoo/wiki/Contributing#reporting-issues)
+* Use this [template](https://github.com/odoo/odoo/tree/9.0/.github/ISSUE_TEMPLATE.md)
   when reporting issues. Please search for duplicates first!
 * Pull requests must be made against the [correct version](https://github.com/odoo/odoo/wiki/Contributing#against-which-version-should-i-submit-a-patch)
 * There are restrictions on the kind of [changes allowed in stable series](https://github.com/odoo/odoo/wiki/Contributing#what-does-stable-mean)