auv-msgs update

[IgnacioCarlucho]

@bmagyar @decabyte @tfurf @henriqueribeiro @narcispr @dulanad @brunovmenna

Guys, this tries to address some of the comments made on #3
I have tried to keep the changes minimal, changing what most of you agreed on.
Let me know what you think and we take it from there.

[bmagyar]

Could you please sum up your changes and new additions as a recap?

[IgnacioCarlucho]

Bence, yes sorry, you are right.
The mayor changes in this version are:

• All the Req msgs were renamed to Request, as suggested by @tfurf, to give a better idea of what the messages are, for instance now we have BodyVelocityRequest
• Added a WorldWaypointRequest message. I used the old version that Bence showed in Missing messages/field from first release #3, and cleaned it a bit, as was suggested in the discussion. I tried to keep it simple and made it similar to the other Request messages. Basically updated the comments and removed the goal descriptor. And also remade max_speed_percent to be a 6dof velocity limit, and rename it twist_limit (do you think this is descriptive?)
• I also updated the maintainers of the package.

That is all. what do you guys think?

[bmagyar]

As this breaks API for everyone using it we'll have to increase major version number on the release & send an announcement on ROS discourse. I've just approved the changes, unless there are others with objections you are good to merge this.