Weigh renaming action_msgs to action_interfaces

[tfoote]

This is a follow up to the Aggregate Foxy Message API Review

It was flagged that new packages are using the standard _interfaces while this is using the older standard _msgs.

We should trade off whether renaming it is more valuable or leaving things as they are is higher value.

[tfoote]

It would be more consistent to have made the new package follow the newer version of the conventions. However it's still following the old naming convention and that convention is well established and will not disappear soon so it's not going to be something that will be hard to understand.

Changing the name of this package will be disruptive and require changing any and all usages of the message. This is a significant distributed cost for a small mostly aesthetic cleanup. Because of that we should stick with the status quo and keep things as they are.