Whether the periodic table is shown or not should be determined by a widget trait

[CasperWA]

Whether the table is shown or not should be determined by a widget trait "show_periodic_table_of_elements" and that trait is linked with the button.

Originally posted by @csadorf in #203 (comment)

A suggestion from #203 by @csadorf.

This makes sense to me, but to be reliable and useable, the way in which filters are invoked needs to be updated. I.e., using a trait for this in the current state will be no different than the implementation used in #203.