Track runcat position for each source, at each epoch

[timstaley]

cf. https://support.astron.nl/lofar_issuetracker/issues/5228
@bartscheers wrote:
During a Trap run the runcat positions are updated every time. The intermediate results are not stored, we only have the latest values in the runcat table. To enable tracking source association we need to store the temporary weighted averaged positions in the asoscxtrsource table as well, along with the distance, the De Ruiter radius and the variability indices for the associations pairs.

[AntoniaR]

This is an ongoing wish list item but not essential for R7. Moving to the long term milestone.