RF: Small API refactoring

src/libloom/data/index.cpp

src/libloom/data/rawdata.cpp

src/libloom/data/rawdata.h

src/libloom/taskinstance.cpp

src/libloom/taskinstance.h

src/libloom/tasks/basetasks.cpp

src/libloom/tasks/rawdatatasks.cpp

src/libloom/worker.cpp

src/libloom/worker.h