Print Position

This blueprint proposes to introduce a print position command.

When the relevant key (proposal : ^P) is pressed while running a train, the present position of the train will be printed out in a specified file.
Possible options are :
 * file location and name
 * possible print format :
   - full (train distance travelled, lat/long position, tile position, sequence number)
   - as a marker file

This function can be very useful to route builders, providing them with exact information of a location in a route which might need further investigation.

Discussion: http://www.elvastower.com/forums/index.php?/topic/29984-proposal-for-print-position-function/
Roadmap: https://trello.com/c/Q8t9rUuS/379-print-position