Change ActionContainer Array to be ActionContainer

[a2]

This PR removes the + operator in favor of joining Actions in Arrays.

Before:

func bar() -> ActionContainer { ... }
let shortcut = buildShortcut(foo() + bar() + baz())

After:

let bars: ActionContainer = [bar(), bar(), bar()]
let shortcut = buildShortcut([foo(), bars, baz()])

Fixes #3

[a2]

This doesn't actually work because of type constraints:

Using 'ActionContainer' as a concrete type conforming to protocol 'ActionContainer' is not supported