BibEditMulti: several improvements

• Adds name of the task submitter to bibupload task for better history entries.

• Also adds name of the task so that bibsched displays bibupload:multiedit

• Fixes bug with checked records that was causing too many computations to happen

• Now only records displayed in the page are compared to their old versions, saving lots of resources

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>