Kdb import merge

Brings the merging framework to the import command. I commented all the side_value tests because i couldn't find this value in any testdata. 
The reason I added this line is due to the change of the threeway merger. Initially it didn't merge parentKeys because for most backends this will cause a merge conflict (because the parent key contains the path). In order to retain backward compatibility and not to change the behaviour of the merge command, I remove the parentKey before merging.