Initial checkin of proof-of-concept
Set add_dlg transient for main window
Rename script and UI file
Add Debian packaging
Add "dot-xsession" as a sample ~/.xsession
UI & library improvements

- The library now stores its metadata in a JSON file, rather
  than per-directory metadata files
- The library now supports a free-form "notes" text field per entryt
- The number of pages in a piece is displayed in the library.
- The library is sortable by title and searchable by title.
- The PDF conversion workflow has been moved to its own class.
- The program correctly handles the case of an empty library.
- You can now import individual images of pages as well as a PDF.