Make code generation feature more obvious

[rsdunlapiv]

In order to generate code now, you have to start with a basic template like this so Cupid will know what you are doing:

module MyModel
   use ESMF
   use NUOPC
   use NUOPC_Model
end module MyModel

This is really not obvious at all to users. There should be a way to generate code from the menu or some obvious button and it needs to be documented in the user's guide (#24).

[rsdunlapiv]

There is a proof of concept for creating a NUOPC application visually using boxes and lines and generating code from it. Uses the Sirius plugin. Looks like a promising approach.

[rsdunlapiv]

There are new menu option when you right click on a folder in the project explorer: new NUOPC Driver, new NUOPC Model cap, new NUOPC Mediator.