Multi Select on BarChart

# 🌈Feature request

**What is this feature?**
I'd like the BarChart to support selecting multiple bars in the chart. It currently only supports a single selection limiting its functionality.
`selected={{ event: IndexedEvent, column: "singleSelection"}]`

**How should the feature work?**
The BarChart should accept an array of selected events such as:
`selected={[{ event: IndexedEvent, column: "selection1"}, {event: IndexedEvent, column: "selection2"]}`
The BarChart would then apply the selected style to all of the selected events in the array and not just the single event. Shift+Click'ing events would by the preferred method of multiple selecting the events, and possible future support for drawing a box around the desired items.

**Do you have examples or an idea of how it can be implemented?**

**Additional context**
(Add any other context or screenshots about the feature request here)