Creates pqHelpers to store helper functions.

Moves toRoman into it.
Creates folio_to_string from code in pqPages, and stores it in PqHelpers.
Align all elements of status bar to vertical center,
as this make everything properly aligned.
Display page number and png number in status bar.

TODO: pagenum should become imagenum, and pagenum2 should become pagenum
TODO: these fields should also have a QLineEdit that appears when the QLabel is clicked on
TODO: pagenum/pagenum2 are not set until editor is clicked in
In the Notes tab, ctrl-p now adds the book page number, not the image number.