Add an action to select and execute an arbitrary action from a list of actions.

[duhrer]

We have reached the point where nearly all of the buttons/axes on most gamepads are used by the default configuration. For less commonly used actions, it would be helpful to have a menu to launch an action without having to bind it to a button or axis. This is particularly appropriate for actions like:

1. Minimising/restoring a window.
2. Opening a new window/tab.
3. Closing a window/tab.
4. Previous/next page in history.
5. Previous/next tab/window.

Although it's tedious, this could also work for the click and tab navigation. It's not as good a fit for scrolling actions, but these could be handled as though they were responding to a single click from a digital button (like the d-pad).

One thought might be only to present actions which are not bound to an axis/button, but providing the ability to launch any action would be a good start.

[duhrer]

Thinking about this overnight, it makes sense to me to tackle this before the config panel refactor, as it involves selecting and configuring a single action from the range of actions. I'd hope to reuse this work to make the config panel factor easier, or at least to think through how to present the range of configuration options for different actions without resorting to the current system of reused form elements and arrays indicating which actions can use which settings.

[duhrer]

In thinking through "reachability" issues, it seems like we should add a key binding for this action if possible. Will need to research what that involves.