Added onShutdown argument in anticipation of heartbeat detection
Switches from interrupts to polling, moved polls to the `update method
Removed default and global message handlers
Made BurtCan into a template, can now be used with Can1, Can2, or Can3
[!Note]
This PR changes BurtCan from using FlexCAN_T4's interrupt-based mailboxes to a polling-based mechanism. The update method will try to clear the CAN buffer. However, if too many messages arrive in between calls to update(), it can result in significant slowdowns and noticeable latency in message handling.
onShutdownargument in anticipation of heartbeat detectionBurtCaninto a template, can now be used withCan1,Can2, orCan3