Documentation: doc for nix::Entity
Documentation: added doc for NamedEntity
Documentation: modified doxygen config.

Doxygen now generates doc only for front facing objects, their sub classes and the things in nix::util.
Documentation: doc added for EntityWithMetadata
Documentation: doc added for EntityWithSources
Documentation: small addition to EntityWithSources
Documentation: tiny correction in IEntityWithMeta
Documentation: doc added for Block
Documentation: docs for DataArray added
Documentation: doc added for DataType
Documentation: change Doxyfile.in, draf for logo
Documentation: added doc for Dimensions
Documentation: fixed doc for DataArray
Ducumentation: Doxyfile.in update
Documentation: doc update for File
Documentation: doc added for DataTag
Documentation: doc added for Feature
Documentation: changes for File
Documentation: Doxyfile.in doc for static members
Documentation: doc added for Property