Geppetto-UI showcase folders should be excluded from release/production version

[afonsobspinto]

In my opinion, geppetto-ui showcase folders should not be included in the release/production version of geppetto-client.

I support my suggestion with an extreme case which is the canvas showcase, where model.json increases the bundle size in 100 mb (still under evaluation here).

How to handle this?
for manual installations: Change the instructions to exclude showcase examples (maybe with a script?). But keep it optional.
for npm releases: We can use .npmignore