Issue 49 (Update LinuxPackageObjectType ArchitectureTypeEnum)

Resolves #49 

Implements the following proposal:
https://github.com/CybOXProject/schemas/wiki/Proposal:-Change-LinuxPackageObjectType-Architecture-Field-To-ControlledVocabularyStringType


This pull request does the following:
* Sets type of LinuxPackageObjectType's Architecture field to ControlledVocabularyStringType
* Removes ArchitectureType
* Removes ArchitectureTypeEnum