Fixed a file location bug in 'Strip PDF Front' action and added 'Strip P...

The "Strip PDF Front" action had the wrong path to the program pdfimage from the xpdf Brew package. I also added a "Strip PDF from Zip" which will remove the PDF file from a zip of files. That one is fairly project specific, but I thought someone might be able to use it. I just used it on 200 ebook zip files.