Fixed:
* Fixed crash in Samplestats. It would crash if BGCorrect columns were
  present.
* Fixed glitch in Samplevis that allowed clicking the 'Other sequences'
  bars if the input data already contained the 'Other sequences' entry.

Improved:
* The TSSV tool will now drop any sequences that contain anything other
  than A, C, T, and G. If the -A option is given, these sequences will
  still be added to the marker aggregates. Many other tools will fail
  when confronted with such invalid sequences, especially when allele
  names need to be generated.
* In Samplevis, the sequences are now consistently sorted (except for
  some inconsistency caused by a bug in Vega). The sorting is based on
  read counts and is the same as used for the allele tables in Samplevis
  HTML visualisations.
* Added a comment line that mentions genome build GRCh38 and rCRS to the
  genome_position block in the libconvert output. This is mainly for
  documentation purposes; users are free to change this line if they use
  a different reference.
* Minor styling changes to Samplevis HTML visualisations.