Extensive refactor for v1.0 release

[cfcurtis]

Refactoring changes

The codebase was refactored to further separate GUI elements from the processing functionality and add more command line support. The code is now structured as follows:

• cli: Directory containing command line interface modules (just app.py for now)
• gui: Directory containing the wxPython GUI modules
• processing: Directory containing the actual PDF manipulation code, with the following modules:
  • procbase.py: Provides ProcessingBase, an abstract base class for each processing unit
  • mainproc.py: Implements a ProcessingBase class to manage sub-units and communicate with the GUI/CLI
  • pagetiler.py: A renamed version of tile_pages.py (the original single script version of PDFStitcher!), providing the PageTiler processing unit class
  • pagefilter.py and layerfilter.py: Not significantly changed in functionality, but now implement ProcessingBase classes

The following refactoring changes have also been made:

• Unit tests for pagetiler.py are provided in tests/test_pagetiler.py (layer filter tests TBD)
• Previous test code has been moved to tests/integration
• "Private" methods have been renamed with the _funcname convention, with most processing units only defining a run method to be called from the GUI/CLI
• Various references to px renamed to pt to more accurately reflect the PDF base unit

Bug fixes and changes

• Several bugs were solved just by updating the pikepdf version
• Some UserUnit issues have been resolved
• Page rotation was assumed to be the wrong way - this is now corrected
• When adding margins, the origin (0,0) is now inside the margin, resulting in a MediaBox of size (-margin, -margin, width + margin, width + margin). This makes page tiling (particularly with trim values) simpler and less error-prone.
• The latest set of translations from Weblate have been merged in

Build system changes

• Version numbers on various GitHub actions have been updated
• macOS Intel build bumped to macos-12 as 11 has lost support :(
• For Windows, the exe is now built with Nuitka, resulting in a slightly smaller file size and hopefully fewer complaints from antivirus software.
• Finally, the thing that many users have been asking for: Notarization on macOS! I tried (repeatedly and unsuccessfully) to make it work with Nuitka, and have reverted to PyInstaller for macOS.

@mara004 I know you've been away from this project for some time, but I wanted to specifically point out the CLI changes as you did a lot of work in adapting the page tiling stuff. It's not gone, it's just moved to cli/app.py. I'm guessing you've adapted it for your own uses by now, but I wanted to let you know as it's a breaking change.

[mara004]

@mara004 I know you've been away from this project for some time, but I wanted to specifically point out the CLI changes as you did a lot of work in adapting the page tiling stuff. It's not gone, it's just moved to cli/app.py. I'm guessing you've adapted it for your own uses by now, but I wanted to let you know as it's a breaking change.

@cfcurtis Thanks for the info, great to see how this project keeps going!
I've made an excursion to rendering/bindings (pdfium/ctypes(gen), pdfbox/jpype, pdfjs/jspybridge), but might get back to page tiling eventually. :)