provide 'enable pad gaps' option on the 'Sequences must be aligned' warning dialog

if the currently selected set of sequences appear unaligned when the user selects a calculation option that requires aligned sequences, then a 'sequences must be aligned' dialog box will be shown. This dialog could give the user the option of enabling 'pad gaps' if they know the sequences are aligned, or don't care, to save them having to enable the option and repeat the gui operation again.