New literals

[alkidbaci]

• New literals (+datatypes) added #81 :

  • nonPositiveInteger
  • nonNegativeInteger
  • positiveInteger
  • negativeInteger
  • float
  • decimal
  • time
  • gYearMonth
  • gMonthDay
  • gYear
  • gMonth
  • gDay

• Refactoring of literal classes for code reduction

• Updated representation and hashing of OWLLiterals to include the datatype in addition to the value

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Not implemented primitive datatypes (as not seen necessary for the moment):

• hexBinary
• base64Binary
• anyURI
• QName
• NOTATION