Changed isotope image metrics implementations in computing module.
Changed isotope image metrics implementations in computing module.

* Dropped irrelevant tests in computing_test
* Moved data for IsoCalcTest into the class code
* Updated IsotopeMetricsTest

SpatialMetabolomics/SM_distributed,SpatialMetabolomics/SM_distributed,METASPACE2020/sm-engine,METASPACE2020/sm-engine,SpatialMetabolomics/SM_distributed,SpatialMetabolomics/SM_distributed