Fix loading algorithms

During the last day there were some changes to the TQPathMerger which broke loading algorithms in analyze.py

Previously there was also the problem that the python file which loads the algorithm had to be in share/algorithms/, otherwise it wouldn't work.

This MR fixes the loading of algorithms and allows to load algorithms from python files in any location.

For this to work the relativ path (from the share folder) to the python file needs to be given in the config file, i.e.

algorithms: myConfig/algorithms/MyAlgorithm.py

If this is not the intended way, please let me know.

Cheers, Benjamin

PS: This MR was originally !132 (closed), but there the source branch is in a fork and not the upstream repo.