Alerting "success" only when some option is selected and submit is clicked in settings

[Puranjay25]

Fixes #

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:

Previously in settings page when user clicks Submit button without actually changing the Message Pane Colour or Predefined themes it shows a success message.
But now success message will only be displayed when some different colour or theme is selected.

Changes proposed in this pull request:

[samagragupta]

Please fill the details in the PR description.
Also, provide a GIF or Image.

[Puranjay25]

@samagragupta I have filled the details in PR description

[samagragupta]

Please use a more descriptive class name.
Rest looks good.

[Puranjay25]

@samagragupta I have changed the class name

[fragm3]

Please fill the issue number. Use descriptive variable names, indent the code properly