initial spec1.4 implementation

[jkowalleck]

fixes #57

• BREAKING changes
  • Interface \CycloneDX\Core\Spec\SpecInterface became internal, was public api. (via [initial spec1.4 implementation #65])
    This is done to prevent the need for future "breaking changed" when the schema requires additional spec implementations.
• Changed
  • Method \CycloneDX\Core\Serialize\{DOM,JSON}\Normalizers\ExternalReferenceNormalizer::normalize throw DomainException when ExternalReference's type was not supported by the spec. (via [initial spec1.4 implementation #65])
    This is considered a non-breaking change, because the behaviour was already documented in the API, even though there was no need for an implementation before.
• Added
  • New class constant \CycloneDX\Core\Spec\Version::V_1_4 for CycloneDX v1.4. (via [initial spec1.4 implementation #65])
  • New class \CycloneDX\Core\Spec\Spec14 to reflect CycloneDX v1.4. (via [initial spec1.4 implementation #65])
  • Support for CycloneDX v1.4 in CycloneDX\Core\Validation\Validators\{Json,Xml}StrictValidator. (via [initial spec1.4 implementation #65])
  • New methods in class \CycloneDX\Core\Spec\Spec1{1,2,3} (via [initial spec1.4 implementation #65])
    • ::getSupportsExternalReferenceTypes()
    • ::isSupportsExternalReferenceType()
  • New class constant CycloneDX\Core\Enums\ExternalReferenceType::RELEASE_NOTES to reflect CycloneDX v1.4. (via [initial spec1.4 implementation #65])

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from milestone tasks:

• Add spec 1.4 schemas to schemas folder
• Add JSF schemas to schemas folder - used in draft 1.4 as a reference
• Add spec 1.4 schema validation

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