scrollIconTopElement is shown when message window is at bottom

[samagragupta]

Fixes #542

Checklist

• I have read the Contribution & Best practices Guide and my PR follows them.
• My branch is up-to-date with the Upstream master branch.
• The unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

• All the functions created/modified in this PR contain relevant docstrings.

Short description of what this resolves:

When a user is at the bottom of the message window then scrollIconTopElement should shown.

Changes proposed in this pull request:

[samagragupta]

@mariobehling Please review this.