Update ISSUE_TEMPLATE.md to provide better section separation
Update ISSUE_TEMPLATE.md to provide better section separation

The "problem description" section is split into a second section
"Expected behavior" to make it easier to read the issue content.

Change-Id: I7b106989a48916c50ffd461d3ee17f595b3bd0be

eclipsesource/tabris-js,eclipsesource/tabris-js,eclipsesource/tabris-js