Added three new exceptions: DependentPropertiestError, AtLeastOnePropertyError, MutuallyExclusivePropertiesError
Added tests for NetworkTraffic, Process, URL, WindowsRegistryKey and X509Certificate
Added error tests for EmailMessage, NetworkTraffic, Artifact,
Added interproperty checker methods to the base class: _check_mutually_exclusive_properties, _check_at_least_one_property and _check_properties_dependency
Added interproperty checkers to Artifact, EmailMIMEComponent, EmailMessage, NetworkTraffic
Made NetworkTraffic.protocols required
Added X509V3ExtenstionsType class
Use EmbeddedObjectProperty for X509Certificate.x509_v3_extensions
uncomment test_file_example_encryption_error
added _check_object_constrains and properties_populated to base class
added ObjectConstraintError
added _check_object_constrains for File