Separate dependency management per template

[derberg]

Description

Come up with a way to define npm dependencies for each template. Maybe templates should become independent installable packages themselves. Such an approach can be easily simplified for development with Lerna to still keep templates in one repository and be able to download dependencies for all the templates with one command.

Reason
At the moment every single dependency is declared in the main package.json of the generator. So even if you have a dependency that is used in just one template, it is added to the main package. This is, for example, an issue for people that use generator package and write their templates, they take large generator package with dependencies, not needed for their template.