Update issue templates

Author: adumesny

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,23 @@
+---
+name: Bug report
+about: bug report
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+## Subject of the issue
+Describe your issue here.
+If unsure if lib bug, use slack channel instead: https://join.slack.com/t/gridstackjs/shared_invite/zt-2qa21lnxz-vw29RdTFet3N6~ABqT9kwA
+
+## Your environment
+* version of gridstack.js - DON'T SAY LATEST as that doesn't mean anything a month/year from now.
+* which browser/OS
+
+## Steps to reproduce
+You **MUST** provide a working demo - keep it simple and avoid frameworks as that could have issues - you can use 
+https://jsfiddle.net/adumesny/jqhkry7g
+
+## Expected behavior
+Tell us what should happen. If hard to describe, attach a video as well.