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.
* Added only healthy to Targets
This adds a "Only heathly" button to supplement the "Only unhealthy"
button. The two are mutually exclusive.
I've also added a red/green text color to the buttons.
Arguably this could be a toggle instead if folks think this is
worthwhile... Happy to modify it.
* Moved functions above init
* Simplifed code and made prettier
* Appeased codeacy
* Made buttons square
