Users Manual Screenshoots Vector Layers

After some more testing and some help from the texi2dvi mailing list, I think I finally found out the solution for our image size and resolution for both PDF and HTML.

The problem did not lay on the configuration file or texi2pdf settings but in the image files itself. All that is needed to do is to open the screenshots in GIMP and change their print resolution from 72 dpi (the original resolution of screens), to something like 135dpi (we can decide which the more suitable resolution). Also, its needed to remove the width size settings form the rst files for those images.

The good news are that images will show at their original resolution in HTML (below maxwidth of the page) and at a different (more suited resolution) in the PDF.

Please confirm building this before accepting the pull request.