Ability to "select all" in multi-select dropdowns

[brandonreid]

This should be a conditional prop. For certain lists, like tags, we wouldn't enable this since the list is more ephemeral and weird. For things like the State select, having nothing selected is essentially the same as having them all selected, but this serves as a utility for selecting all and deselecting a few to reach an end state (user's often want filter out just the scheduled runs, for example).