This change adds a download link to the printer dialog. The contents
of the download will be the raw bytes written to the parallel
interface. Note that often these bytes will have the high-bit set
causing the contents to look like gibberish.
However, this is extremely handy because it allows one to turn the
printer output into a PDF:
1. In Appleworks (for example) configure an Apple ImageWriter in slot
1 and print a file.
2. Download the printer output.
3. Download the header file from https://github.com/AppleWin/AppleWin/files/1168047/ImageWriterEmulator-NoLF.ps.txt
4. In Linux, run:
```shell
$ cat ImageWriterEmulator-NoLF.ps.txt raw_printer_output.bin | ps2pdf - printer_output.pdf
```
Note that the parallel port emulation in apple2js does not yet support
Print Shop, so I haven't been able to test that out.
