Forward signals

Forward SIGINT and SIGTERM to rawdata-download, from rawdata-downloader and rawdata-procedures.

* to avoid camera data corruption when rawdata-procedures receive a signal while fsck is running
* to avoid leaving an eSATA port disabled on localhost (signal received during hotswap)
* to allow resetting multiplexers before exit

Using kill in rawdata-procedures is not possible because rawdata-downloader is run with sudo. Therefore a FIFO is used instead.