Feature request: Add message component syntactic sugar.

[filipstachura]

This one is very easy. The more abstract the better. Please before implementation go through: https://semantic-ui.com/collections/message.html

Below simple implementation from our current app:

render_warning <- function(header, content) {
    div(class = "ui error message",
      div(class = "header", header),
      content
    )
}

Requirements:

• optional icon parameter
• IDEA: if content is a list then use List Message
• support for Dismissable messages (This requires javascript!)
• support for additional classes (e.g. Attached, Floating, Warning, Positive, Size)

[krystian8207]

@olgamie @dokato can you confirm existing messagebox function closes the issue?