Create ISSUE_TEMPLATE.md

Provide issue template which will make it easier to remember all the details to provide when reporting an issue.

ISSUE_TEMPLATE.md

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+### Setup
+
+- Browsers and versions:
+- MediaWiki version:
+- Database version:
+- PHP version:
+- Foreground version:
+- Extension version (if connected to the issue):
+
+### Issue
+
+Detailed description of the issue goes here.