Add New Project menu item and open it to extension developers to add project types

[velara3]

Add a new menu item called New Project and then allow extension authors the ability to register their own project type and handler for it.

For example, the Electron team can create an extension that creates an Election project. When selecting that option they then create the folders and projects and open that project.

File > New Project >

• Electron
• Angular
• React
• anything else

[dgchrt]

I've been looking for something exactly like this. Please make sure to also have at least one built-in category for TypeScript projects.

[reregaga]

Related: #365