All demos should be adaptive / mobile

[sonnyp]

We want the GNOME ecosystem to be adaptive. Workbench demos are meant to be copy pasted and reused.

See workbenchdev/Workbench#677

We should make all Library demos adaptive and work well on 360 screen width.

There is 2 additional things we can do to enforce this:

• Make Workbench mobile friendly so the Library entries will be consulted there and people will report issues.
• CI that checks the size of the preview window for 360px