Fixes of minor issues that are relevant when correcting with large k-mer sizes and low coverage regions

Python 3/2 compatibility for sga-preqc-report

added new parameter -O --count-offset to only make a correction if the new kmer has a count higher by N than the old kmer. Default 1. Set to >1 to avoid e.g. correcting a kmer seen 3times with one that occurs 4times.  Changes in Algorithm/ErrorCorrectProcess.cpp Algorithm/ErrorCorrectProcess.h SGA/SGACommon.h SGA/correct.cpp

added option to specify random seed

Kmer Count along a sequence (kmer-plot)

ktrns:Algorithm/ErrorCorrectProcess.cpp;Algorithm/ErrorCorrectProcess.h;Algorithm/KmerOverlaps.cpp;SGA/SGACommon.h;SGA/correct.cpp;Thirdparty/multiple_alignment.cpp: Overlapp correction is adapted to introduce less errors. Parameters 'X' and 'M' are introduced.

ktrns:src/Algorithm/ErrorCorrectProcess.cpp;src/Thirdparty/multiple_alignment.cpp;src/Thirdparty/multiple_alignment.h: Updated overlap correction to only flip bases if there is a minimum coverage of 3 and no more than one possible flip.

ktrins:src/Algorithm/ErrorCorrectProcess.cpp: Kmer-correction bugfix. A ...

ktrins:src/Algorithm/ErrorCorrectProcess.cpp: Kmer-correction bugfix. A base is only corrected if there is no ambiguity.

when extracting the reference sequence from VCF, should use REF field rather than ALT for the event length