Add status field to action result messages

[sea-bass]

Public API Changes
N/A

Description
This goes along with RobotWebTools/rosbridge_suite#953, in which a status field was added to the action_result message.

It also adds a setCanceled() helper function to the Action class to wrap the setting of the right status in cancellation settings.

[EzraBrooks]

I'm like half asleep and on a plane right now so maybe I'm missing context, but I'm not sure I grok what's going on here. Is this an action-server-side feature or action-client-side?

[sea-bass]

I'm like half asleep and on a plane right now so maybe I'm missing context, but I'm not sure I grok what's going on here. Is this an action-server-side feature or action-client-side?

This is a server-side feature.

For context, take a look at RobotWebTools/rosbridge_suite#920 and the PR that tries to solve it (RobotWebTools/rosbridge_suite#953).

Basically, there are 2 new things:

1. Now the action_result message carries a status with it (hence the additions to the setSucceeded()/setFailed() functions here)
2. Also, when you cancel a goal client-side, instead of the client automatically aborting the goal, the server is responsible for telling you that it was canceled (hence the addition of the setCanceled() function here).