Support for multiple submissions under one user

• Modified ParticipantDatabase to optionally strip off _# from guid
  when doing search for Participant. This is to handle case where
  single participant has multiple submissions to CELPP. Issue #98
• Switched os.getlogin() calls to pwd.getpwuid(os.getuid())[0]
  cause os.getlogin() was raising OSError on Travis. Issue #102
• Fixed bug where evaluation task completed email had log messages
  from other evaluation task emails in them. Issue #99
• Updated readme.txt file in challenge data package to reflect
  use of new_release_structure_sequence_canonical.tsv instead of
  new_release_structure_sequence.tsv file. Issue #97