simulation organization and cleanup

- new modules/simulation directory to collect all simulators and related modules
 - new Tools/simulation directory to collect and organize scattered simulation submodules, scripts, etc
 - simulation module renamed to simulator_mavlink
 - sih renamed to simulator_sih (not a great name, but I wanted to be clear it was a simulator)
 - ignition_simulator renamed to simulator_ignition_bridge
 - large sitl_target.cmake split by simulation option and in some cases pushed to appropriate modules
 - sitl targets broken down to what's actually available (eg jmavsim only has 1 model and 1 world)
 - new Gazebo consistently referred to as Ignition for now (probably the least confusing thing until we fully drop Gazebo classic support someday)

Tools/simulation/flightgear/sitl_run.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+
+set -e
+
+if [ "$#" -lt 4 ]; then
+	echo usage: sitl_run.sh sitl_bin model src_path build_path
+	exit 1
+fi
+
+sitl_bin="$1"
+model="$2"
+src_path="$3"
+build_path="$4"
+
+echo SITL ARGS
+
+echo sitl_bin: $sitl_bin
+echo model: $model
+echo src_path: $src_path
+echo build_path: $build_path
+
+rootfs="$build_path/rootfs" # this is the working directory
+mkdir -p "$rootfs"
+
+export PX4_SIM_MODEL=${model}
+
+echo "FG setup"
+cd "${src_path}/Tools/simulation/flightgear/flightgear_bridge/"
+./FG_run.py models/${model}.json 0
+"${build_path}/build_flightgear_bridge/flightgear_bridge" 0 `./get_FGbridge_params.py "models/"${model}".json"` &
+FG_BRIDGE_PID=$!
+
+pushd "$rootfs" >/dev/null
+
+# Do not exit on failure now from here on because we want the complete cleanup
+set +e
+
+sitl_command="\"$sitl_bin\" \"$build_path\"/etc"
+
+echo SITL COMMAND: $sitl_command
+
+eval $sitl_command
+
+popd >/dev/null
+
+kill $FG_BRIDGE_PID
+kill -9 `cat /tmp/px4fgfspid_0`