Update ISSUE_TEMPLATE.md (#747)
Update ISSUE_TEMPLATE.md (#747)

## Changes:

- add more fields
- change formatting of headings
- additional clarification for certain fields
htalat/Excalibur,excaliburjs/Excalibur,excaliburjs/Excalibur,excaliburjs/Excalibur,htalat/Excalibur,htalat/Excalibur