Reorganize repo into two subfolders

In https://github.com/KiCad/kicad-templates/pull/13 we concluded that a reorganization of the template repo was needed.

I have splitted templates into projects and worksheets and updated CMake scripts accordingly. BEWARE I am not fluent in CMake language and I don't know the best language practices. Please check that in depth.

Also, default template file may have moved and that could require devs intervention.

Any improvements sugestions or comments? Thanks!