Fix bug and change interface of getMaxWeight and move track/cluster encoding parts to MarlinUtil

[dudarboh]

Make getMaxWeight functionality templated that allows passing any comparator. Moving track/caluster weight encodings functionality into MarlinUtil

Added with LCIO v02-18 (https://github.com/iLCSoft/LCIO/releases/tag/v02-18) utility methods to extract the highest weight for LCRelationNavigator are not working properly.

1. getMaxWeightIt() must return max_element in every if branch, otherwise passed "weight" parameter is just ignored
   

   LCIO/src/cpp/src/UTIL/LCRelationNavigator.cc

   Lines 72 to 81 in 2a0d5d1

   	if (weightType == "track") {
   	std::max_element(weights.begin(), weights.end(), [](float a, float b) {
   	return (int(a) % 10000) / 1000. < (int(b) % 10000) / 1000.;
   	});
   	} else if (weightType == "cluster") {
   	std::max_element(weights.begin(), weights.end(), [](float a, float b) {
   	return (int(a) / 10000) / 1000. < (int(b) / 10000) /1000.;
   	});
   	}
   	return std::max_element(weights.begin(), weights.end());

2. Every new function that uses std::string& weightType as an argument, must have an empty string as a default.

We have discussed with @tmadlener that it would be nice to keep the functionality as general as possible in LCIO and have track/cluster specific weight encoding parts in the MarlinUtil, as these encodings are defined only to some specific LCRelation collections which are created by MarlinReco.

This PR fixes bugs described above and changes the interface to be more generic allowing an arbitrary comparator function as an argument instead of previously string parameter.

Two specific comparator function for track and cluster weights will be added to the MarlinUtil soon.

BEGINRELEASENOTES

• getRelatedTo(From)MaxWeightObject() and getRelatedTo(From)MaxWeight() now accept generic decode function of float(float) signature as a second argument, which specifies how to decode the weight. Default option is identity function (just compares weights as they are).
• Helper functions to decode and encode "track"/"cluster" specific weights from PFO-MCParticle LCRelation collection are added to MarlinUtil in MarlinUtil#36.

ENDRELEASENOTES

[tmadlener]

Just a few minor comments / questions (see below).

Maybe one thing that should be added to the docstrings, is the requirements for the CompareF, i.e. the signature is bool(float, float) and that the return value should be true if the first argument is "less" than the second.