Add IsCloseButtonEnabled to MessageBox and make button border padding configurable

[Difegue]

Pull request type

Please check the type of change your PR introduces:

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the current behavior?

Every instance of ui:MessageBox comes with a Close button that can't be removed.

Issue Number: N/A

What is the new behavior?

• Padding of the MessageBox can be configured instead of the hardcoded 12
• Close Button can be hidden in case you only need the Primary/Secondary Buttons

Other information