Add option to add_widget() to not append node

[jhpedemonte]

To go along with issue #216 and the current impl of remove_widget, the function add_widget should have an option to skip the call to append(). This will allow us to use gridstack in a situation where the DOM nodes are already in place and we don't want gridstack to move or destroy existing nodes.

[karellm]

Is there a reason this was closed @troolee ? I would really like that option, in our current implementation we are forced to overwrite addWidget which is quite hacky. Thanks!

[troolee]

Hi @karellm

method makeWidget has been added for that purpose https://github.com/troolee/gridstack.js/tree/master/doc#makewidgetel