Refactor joint properties data structure (#110)

[scchow]

This PR addresses #110 for Noetic:

• Refactored joint_properties to use a map of maps for streamlined access to joint properties
• Removed JointProperty struct as information contained is redundant.
• Updated tests to account for new signature for getJointProperties().

After doing incorporating these changes, I realized that this would significantly change functionality in the following ways:

• Changed function signatures for getJointProperties()
• Removal of JointProperty struct

As a result, if this PR gets merged, I will need to update my PR in MoveIt! (https://github.com/ros-planning/moveit/pull/3359) to account for the modified data structures here.

Since the backport that I did for ROS1 is relatively new, merging this shouldn't cause many problems, as I doubt anyone else has started using the features I backported 2 weeks ago.

However, we should be careful about doing the same for ROS2, since it will likely break things in MoveIt2 (such as the same test in MoveIt2 here and as well as anyone else who were relying on the original joint properties data structure/function signatures).

I can definitely work on a similar PR for ROS2, but wanted to get your thoughts first.

Cheers!

[rhaschke]

Please adapt your MoveIt PR accordingly.

[rhaschke]

Thanks for cleaning this up!

[scchow]

Thanks for the helpful comments! Good call on using the descriptive aliases.

I'll put together a similar patch for the ROS2 branch if I can find some time this/next week.