- Changed the type of the added and deleted trees in the FSStatus type. Both
  are now FSTree instead of Mergetree. In both cases the files are in only one
  tree, so then it does not make much sense to keep this info in a mergeTree:
  i.e. if a file was added in the newTree then there is no useful information
  about this file in the oldTree, so there is no point in keeping the MergeTree
  containing this info

- Removed the individual functions working on two FStrees, and renamed the
  ticked ones (that worked on the mergetree as input) to the regular name.