Dynamic PPM source enhancement

[unxs0]

Provide a way to for AIS-catcher to get a new -p value from some IPC method.

Why? Since inexpensive RTL dongles (that developing nation users can better afford e.g. RTL2838) have a very wide crystal drift depending a lot on temperature among other factors. And since a new PPM value can easily be calculated by different means including using cell tower and even approximated by environment temperature. It would be useful to be able to set the -p value that a running AIS-catcher instance is using. As long as it can be updated every 5 minutes without impacting performance it would be a great help.

Thank you for your consideration. Cheers!