Find and parse .action files as required

[chfritz]

• in addition to .msg and .srv files we can now also require the
  generation of message classes for actionlib files (.action). This
  is in preparation for supporting actionlib as well.

  Example:

rosnodejs.initNode('/my_node', {
  messages: ['std_msgs/String', 'turtlesim/Pose'],
  services: ['std_srvs/SetBool', "turtlesim/TeleportRelative"],
  actions: ['actionlib/TwoInts']
}).then((rosNode) => {
...

Afterwards, the message handler class can be retrieved from the registry like for services:

const action_goal_handler = rosnodejs.require('actionlib').action.TwoInts.Goal;
const action_result_handler = rosnodejs.require('actionlib').action.TwoInts.Result;
const action_feedback_handler = rosnodejs.require('actionlib').action.TwoInts.Feedback;