Filters: superclass for filters and some standard filters
Block: use new filters in method simpleTags()
Add missing virtual dtors to classes in nix::base

This should fix #32
Further my IDE auromatically corrected some indentions
rename of delete methods in file*
rename of delete methods in section*
rename of delete methods in Property*
rename delete methods in Source* and Block* files
rename delete methods in DataArray* files
rename of delete methods in SimpleTag* files
removed old TestEntityWithMetadata
add new test for base entity class
new test for EntityWithMetadata
activate new tests
removed old TestEntityWithSources
add new tests for EntityWithSources
update with new Test
rename removeSource to deleteSource in TestEntityWithMetadata