Refs #4059 Work in progress: Conversion to use Namespaces

core/DataTable/Map.php

core/DataTable/Simple.php

core/Period.php

core/Period/Month.php

core/Period/Week.php

core/Period/Year.php

tests/PHPUnit/Core/DataTable/Filter/TruncateTest.php

tests/PHPUnit/Core/DataTable/MapTest.php

tests/PHPUnit/Core/DataTableTest.php

tests/PHPUnit/Core/Period/RangeTest.php

tests/PHPUnit/Core/Period/YearTest.php

tests/PHPUnit/Core/PeriodTest.php

tests/PHPUnit/Core/TaskSchedulerTest.php