* Add a keyboard shortcut to toggle all exemplars
Sometimes it's hard to see the quantile line behind all the exemplars.
This commit adds a `d x` keyboard shortcut to toggle exemplar visibility
on all prometheus queries. Unlike with legends, the logic is simpler
and it does a pure toggle as opposed to "majority toggle" as with legends.
Since exemplars might not be loaded, this also requires refreshing the data.
For the same reason, toggling a single panel is not supported, as it will
make the panel data out of sync with the rest of the dashboard.
* Use "p x" to navigate to panel explore rather than just "x"
It's more consistent with other panel level shortcuts.
It also doesn't conflict with the global "x" to toggle exemplars that way.
Ivan Babrou
