Support for custom template directories

[malept]

There are a bunch of framework-specific Electron boilerplates, e.g., for React & Vue. Perhaps we should allow initializing using a custom template directory?

[malept]

I was thinking about this today in the context of the current init command. As it's written, there's an optional lintstyle attribute that chooses whether to copy in an .eslintrc (for the airbnb coding standard). You can't really replicate that with a template directory, unless you plan on duplicating files (which I'd like to avoid doing en masse), there would need to be some logic involved in copying.

So, my current idea is to define a mini framework for creating boilerplates. It would look something like this:

• A package would be named electron-forge-init-$TEMPLATE_NAME, e.g. electron-forge-init-backbone
• electron-forge-init-$TEMPLATE_NAME - The CLI. electron-forge init $TEMPLATE_NAME [args...] passes the args to this
• tmpl/ - The folder where all of the templated files are stored. Dotfiles are prefixed with _ instead of .
• The electron-forge module would have public helper methods to facilitate copying files/folders to the correct places.

init would need to change to have a required templatename argument. The existing template in Electron Forge would be known as default. (Or figure out how to allow the templatename to be omitted and actually default to default - not sure how difficult that would be.)

@MarshallOfSound what do you think?