MANTA-20 new basecall error object

incorporates sequencer error and snp prob
MANTA-20 clean up qscore init
MANTA-20 add read size to sv evidence
MANTA-20 consolidate split/paired support tests
MANTA-20 add split reads into fragment lhood
Add debug option to run single edges in GSvC
MANTA-20 account for N's in split lhood compute