Split ZipLoader classes

[abukaj]

_ICData.ZipLoader* classes have two responsibilities:

• IC data loading:
  • .extractSessions(),
  • ._findAndOpenZipFile(),
  • .DATETIME_FIELDS,
  • .KEY_TO_STEM,
• loaded data wrapping and analysis:
• .wrapVisits(),
• .wrapLog(),
• .wrapEnv(),
• .wrapHw(),
• .extractAndWrapAnimals(),
• .extractAndWrapGroups(),
• .VISIT_ID_FIELD.

Classes should be split (possibly with use of TDD methodology).