add missing sys/select.h include

libspacemouse.h had an include which pulled in this missing include and
it shouldn't be relied upon.
add AXIS_MAP_SPACENAVD macro for mapping strings to axis
rewrite event parsing

Move axis_event to run_event_command() and members belong to polarity. Change axis_map accordingly. Slightly simpler event parsing.
initialize mouse_event to zero instead of memset call
Merge branch 'feature/axis_map' into develop
add '!' alias to switch for led command
update help message with '!' alias for switch