[Enhancement] Adding 'Close' Button to the panel

[happyshows]

and also notify shiny if a box has been closed for post processing.

[harveyl888]

I've thought about this too and experimented with this a little while ago. When I have some time I'll pull back the old code and see if I can get it done.
Thanks.

[happyshows]

Here is another example available in shinydashboard but not documented, in case it helps.
[https://github.com/rstudio/shinydashboard/search?utf8=%E2%9C%93&q=data-widget%3D%22remove%22]