vidjil.cpp: '-a' option also sets very_detailed_analysis

To actually output 'out/seq/sequences.fa-*', we need to run this somewhat old code
vidjil.cpp: outputs also the representative in 'out/seq/sequences.fa-*'
core/representative.cpp: put 'representative' in the label
tests/testRepresentative.cpp: update unit tests
vidjil.cpp, doc/algo.org: explains that the -n/-e clustering is not exported in vidjil.data

Additionaly, use everywhere 'clustering' instead of 'clusteri[sz]ation'