After removing the checkbox in #3913 the only remaining element that
looked like it was the new Show Annotations checkbox on the Alerts page.
Which in turn didn't look like the Enable query history checkout on the
graph page. So:
1. This takes the Enable query history button as canonical.
2. Updates the show annotations button code to match it.
3. Simplifies the JS for the checkbox.
James Turnbull
Julien Pivotto
Sam Starling
Fabian Reinartz