We can't control the size of the produced images when using PDF Plugin

[max]

When doing advanced PDF collections using PDF Plugin to convert pdf to images we cannot control the size of those pictures. And in fact they need to be bigger.

Do we add the options in the PDF Plugin and make them available only we convert-to image(jpg,gif,etc...) is selected? We may have to think of other options to give the user more room for customization...

[davidb]

For now, make value used fixed to something bigger (say 800). Look to make this a plugin option for 2.82

[ak19]

When PDFPlugin now converts PDF pages to images it no longer uses the default screenviewsize of 500 but sets it to 1000. This didn't work previously because the convert_to pattern-match on pagedimg failed. It turned out that the pattern should have been looking for PagedImage instead.