selectAll only selects items on current page

[David-Mulder]

Per title, problem is that selecting all items would require a new function on the data-source that requests all ids~ Relatively easy to do when using the ids->getByIds approach, harder with just the get approach.

[David-Mulder]

As selection behaviour is far more abstracted to <paper-datatable-card> since version 0.5 this might actually be do-able differently now.

[David-Mulder]

And I take that back, I can build a neat implementation where I would allow selection of all items, but all items except for one becomes impossible again then. So back to a getByIds approach.