Use search path for files in tracer config relative to location of the config file

[nightlark]

I noticed that trying to run TraceR with a config file in a different directory (e.g. ../tracer_config or subfolder/tracer_config) results in an error tryign to open the map files listed in the config file. Looking for referenced files relative to the location of the config file would allow more flexible choices for where to run tracer (+ default location of output files not cluttering a checked out git repo) and make it easier to use (no requirement to run from the same directory as the config file).