Added fields for encryption and compression information associated with a FileObj.
Added CipherType to cybox_common to enumerate common encryption ciphers, then refer to it from the FileObj.  Also renamed FileObj Encryption_Key to Decryption_Key to be more precise about it's purpose.
Merge remote-tracking branch 'upstream/version_2.1' into issue_237

Conflicts:
	cybox_common.xsd
Merge remote-tracking branch 'upstream/version_2.1' into issue_237

Conflicts:
	cybox_common.xsd
Merge pull request #259 from mobhutu/issue_237

Issue 237: Added fields for encryption and compression to FileObj