BibEdit: make AJAX calls synchronous

• Currently, AJAX calls are executed asynchronously but a check is made on the server to keep order of modifications. An error occurs if two modifications are made fast in the user interface and the second one reaches the server before the response for the first one has been received in the client side.

• Change AJAX parameter async to false in most of the calls to avoid these kind of errors.

• Tests on large number of operations and big records seem to indicate that loss of performance is not perceivable