Ros1 imu backport

[idlebear]

Hi there -- sorry if I'm stepping on any toes, but I needed to get IMU data for the vesc running against a TX2.

Completed a backport, basically pulling from the ROS2 branch as necessary. Preliminary testing looks good, on Melodic/18.02, though I only have a sample set of one.

I've got a few other minor adjustments I've had to make to quiet down a few warnings, but they're all in another branch. I'll do another pull req if you want them too.

Where possible, I tried to retain formatting, but it appears my autoformatter has made some white spaces changes here and there. Do you have a preferred formatter?

[JWhitleyWork]

Changes seem pretty simple. Will merge if CI passes.

[idlebear]

It was a fairly straightforward port. I've made some other minor changes since to make it play nice with some of the ROS1 eco-system, some more necessary than others:

• a default IMU frame, with rosparam init -- quiet error message and allow for static TF
• default (high) variance for unmeasured/reported poses -- robot_pose_ekf didn't work with null values
• shortened message queues as old data was causing some issues (may not be necessary)
• invert Y on servo - allows reverse of server operation (probably needs a better name)

I haven't submitted any of these -- let me know if you think they're useful and I'll submit a follow-up pull

[idlebear]

Maybe hold that thought -- besides the build issue, there's another performance issue that these changes are causing. After a short interval (minutes of operation), the VESC stops responding to RPM requests. I'll reopen this request once I figure out what's going on.