shows error dialog when reader.open failed
disabls the close button in header when the book is not opened
shows help texts when question mark button in header is clicked
removes unecessary templates (modal.html)
shows progress bar dialog in opening book
bugfix: error message dialog was not opened because the dialog conflicts with the progress-bar dialog
adds unarchiver.enablesRangeRequestInPdf option
adds configuretion dialog template
updates the query string params section in README
implements the configuration dialog (appears when a user click the footer config button)