TDMA MAC improvements and cleanup

Breaking Changes

• The tdma_test_mac_node has been removed. A superset of its functionality is now available in the tdma_scripted_node
• The tdma_nav_header_node has been removed. A superset of its functionality is now available in the tdma_advanced_node and tdma_scripted_node
• Added new python dependency: croniter

Improvements

• Moved common MAC functions to mac_utils.py
• Simplified base tdma_node and made it easier to derive more advanced TDMA MAC nodes
• Added new TDMA MAC nodes:
  • tdma_advanced_node, which inherits from tdma_node and adds dynamic reconfigure parameters, soft-mute, and modem/transponder pings
  • tdma_scriped_node, which inherits from tdma_advanced_node and adds the ability to read parameters from a "test plan" yaml file
• Modified CI tests to use a common base test template
• Added basic tests for new TDMA nodes