Support Security Information

[SegaraRai]

Support security information.

• Implement serialization and deserialization of security information
  (to store security information into metadata)
• Implement DGetFileSecurity and DSetFileSecurity in LibMergeFS
• Implement DGetFileSecurity and DSetFileSecurity in MFPSFileSystem
• Implement DGetFileSecurity and DSetFileSecurity in other plugins which do not support security information