Add de-dupe cover option for landscape alignment

[resendeBruno]

• fix Empty cover page #433
• fix First page duplicated  #557
• fix [Feature Request] Add option for the insertion of a single blank page to correct alignment of two-page spreads #640

--prefercoverfile use cover.jpeg (or cover.png) as the cover instead of the first item on the folder

--nocoveraspage deletes the image selected to be a cover so it doesn't become a page inside the book. Useful when the epub reader shows the cover as the first page

--author allows you to name the author yourself

[resendeBruno]

--nocoveraspage probably fixes this

• First page duplicated  #557

[axu2]

I've split this up into multiple PR to make reviewing easier. Please make a new PR for prefercover, since page renaming changes have broken that part of the PR.

• look at Unsupported directory structure cover #662

I added the GUI stuff as well. It's a lot of changes done automatically by Qt Creator.

Please test:

https://github.com/axu2/kcc/releases/tag/v5.7.0-dedupe

@resendeBruno @diogo7santiago @alexandrealbuquerque000 @senecaFallsConvention @peiskios @PrinceSeven