launch: APM2: Add node.launch and update apm scripts to use it.

Issue #144.
launch: PX4: use node.launch in PX4 scripts.

Also remove px4_local_gcs.launch: please use
`roslaunch mavros px4.launch gcs_url:=udp://@localhost` instead.

Issue #144.
extras: launch: Use includes.

Fix #144.