Solving complex CDR3 cases

Non-canonical CDR3 workaround

• Fix CDR3 end calculation when J segment reference point is at the boundary or J segment conserved residue is absent with downstream J sequence aligned
• Implement CDR3 start calculation in case V-CDR3 region was not identified by IgBlast
• Add "canonical" CDR3 flag which tells if CDR3 starts with C and ends with F/W
  • Add corresponding filter to output (--allow-noncanonical)