replay: add replay module, build for sitl_default, but do not load on startup

This adds a new module that does:
- read an parse an ULog file, given via ENV variable 'replay'
- apply all parameters from the log file
- read and apply user-defined override parameters from a file
- publish all messages in 'real-time' from the log file and add a constant
  offset to the timestamp to match the system time.
- apply changed parameters in the log (which are not overridden)

cmake/configs/posix_sitl_default.cmake

@@ -52,6 +52,7 @@ set(config_module_list
 	modules/param
 	modules/position_estimator_inav
 	modules/local_position_estimator
+	modules/replay
 	modules/sdlog2
 	modules/sensors
 	modules/simulator