push: add `pushoperation.bkresult` This attribute will be used to carry the result of the bookmark push (when the `push` function will effectively be doing any bookmarks pushes)

push: pass list of bookmark to `exchange.push` Currently stored but not unused. This parameter will control bookmarks explicitly pushed (added to the server if missing).

exchange: import bookmarks as bookmod Using the original names makes it difficult to use `bookmarks` as a variable name.