Add support for solution/project scaffolding

[BalassaMarton]

This came to mind while developing our internal SDK. If you look at a monorepo like dotnet/runtime, when one needs to add a new solution, there are steps that go beyond dotnet new. These include creating Directory.Build.props files, adding repo-level properties, creating standard directories like src, test, benchmarks, etc. This could be streamlined with a new command that can at least create the files and directory structures.

Syntax

please scaffold <TemplatePath> <TargetPath> [--<VariableName> <VariableValue>]*

Behavior

1. Take the directory at TemplatePath and copy it to TargetPath
2. Recursively replace the supplied variables with their values using some lightweight templating engine like Handlebars.Net

Notes

Not sure how to accomplish the 'add repo-level properties' part, eg. when scaffolding a new library called EpicLibrary, I want to add an EpicLibraryVersion property to some repo-level .props file. We could add a mechanism similar to Regedit's .reg files, however this is probably out of scope for a first version.