Add new screen options to allow filters to be hidden

[frankiejarrett]

As UI enhancement originally discussed in #306, we should be giving users the option to hide filters they don't find useful, or even hide them all!

1. Only show filters that are checked.
2. All filters should be checked by default.
3. If all filters are unchecked then we should also hide the Filter button.
4. When filters are hidden, their labels in the list table should no longer be hyperlinks, because there would no longer be any visual indicator that the results are being filtered, nor would there be an easy way to reset/clear the selection.

[frankiejarrett]

Point no. 4 above is really up for debate. I just wanted to raise it as a UX concern, we could still include labels as links and probably be OK. Just need to weigh the pros and cons.