Table action menus

Table actions are currently displayed as individual buttons above the table. This is fine in most cases such as when there are only a few actions. However, there are cases where it would better if we had the ability to place some actions into a drop-down menu, similar to how the row actions work. The most obvious scenario is when there are many table actions.

There are currently no tables in horizon that would require a table action menu, but those who create their own panels and dashboards built on horizon would benefit from this ability.