Add "New Title" column with {} references

[andrasfuchs]

The new files will get their filenames from the "Table of Contents" column value in the "Select Sections to Split Off" table. It would be great to have more control and see beforehand what the new books' title will be. Ideally we could format it with references like "{Title} - {PartNumber} - {ToC}" to generate something like "The Science of Interstellar - 0005 - 1 A Scientist in Hollywood: The Genesis of Interstellar" instead of just "1 A Scientist in Hollywood: The Genesis of Interstellar". It would be much better, because this new formatting would keep the order of the sections (unlike the current naming) and the whole Calibre library more organized.