security: Add configuration based validator

configuration file format can be found at: http://redmine.named-data.net/projects/ndn-cpp-dev/wiki/CommandValidatorConf

Change-Id: Icc2725f349aed7513f35f2cccdcd4463fadeef31
security: fix CommandInterestValidator bug (no check on signature type)

refs: #1423

Change-Id: Ida49fde746c5766373ea6fb174f82598e16915d1