IDE should not quit on closing of last open sketch (workspace)

[paschlie]

• The App should not quit upon the closing of the last open editor window; instead it should open an open-project window, including an option to create a new project

If one considers the app's file menu; it really makes no sense to be forced to open a new file, prior to closing a currently open one; but if once the currently open file is closed, the app quits, then the file menu becomes inaccessible and can't be used to open another; which is not really a useful nor thereby a desirable behavior.

[kittaakos]

Duplicate of #758.

I updated the other issue with the acceptance criteria and moved the conversation from here to there.