Fixed #51 and added custom fields to contact data source

CHANGELOG.md

...ataProcessor/FilterHandler/AbstractFieldFilterHandler.php

Civi/DataProcessor/FilterHandler/CaseRoleFilter.php

Civi/DataProcessor/FilterHandler/ChecksumFilter.php

...ataProcessor/FilterHandler/ContactHasMembershipFilter.php

Civi/DataProcessor/FilterHandler/ContactInGroupFilter.php

Civi/DataProcessor/FilterHandler/ContactTypeFilter.php

Civi/DataProcessor/FilterHandler/ContactWithTagFilter.php

Civi/DataProcessor/FilterHandler/DateFilter.php

Civi/DataProcessor/FilterHandler/MultipleFieldFilter.php

...Processor/FilterHandler/PermissionToViewContactFilter.php

Civi/DataProcessor/FilterHandler/SimpleSqlFilter.php

Civi/DataProcessor/FilterHandler/WorldRegionFilter.php

Civi/DataProcessor/ProcessorType/AbstractProcessorType.php

Civi/DataProcessor/Source/AbstractCivicrmEntitySource.php

Civi/DataProcessor/Source/Contact/ContactSource.php

info.xml