Actions are a powerful feature for defining parts of the UI and for

allowing extensions to customize it further. This change builds upon

this framework by giving users their own control over which actions they

want ready access to.
The Unified Banner now defines an area for Quick Access actions. These

are chosen from a menu to the right of the bar, and can allow users to

place any Quick Access actions there.
Quick Access actions are new action classes placed in a quick-access

attachment point. They're generally buttons (though in theory, menus or

other action types could also be placed), and contain some additional

state used for RB.ActionView and RB.PageView.
A QuickAccessActionMixin helps with defining these actions, and can be

mixed in along with another action in order to convert it to a Quick

Acccess action.
There are currently four Quick Access actions defined: Create Review,

Edit Review, Add General Comment, and Ship It. These will allow users

to place any or all of these actions at the top of their browser window

for easy access.
Customization is done through the menu at the right of the bar,

presented as a checklist of all available actions. Toggling these

actions will put the actions (already technically present in the bar but

hidden and disabled) into an enabled state, allowing normal visibility

rules to take over. Upon closing the menu, the new list of actions will

be saved to the user's settings. This makes customization really easy

and fast.
In the future, we'll be able to add optional actions for new features,

such as a "Ship It and Archive" or similar.

Unit tests pass. There's room for more tests to be written, but

they'll be handled separately.
Tested this with a user without any Quick Access settings, a user

with settings, and anonymous users.
Tested adding all the actions we currently supply, and verifying

that they only showed up if enabled for the user, regardless of

any state calculations done in JavaScript. Also verified that those

state calculations were reflected properly when actions were enabled.
Tested on small browser windows and mobile sizes. There is work that's

needed for really optimizing on mobile, but it's beyond the scope of

this work.