Optionnally resize/compress pictures before sending
Description of the new feature
It would be nice to allow sending degraded version of pictures. Most mobile messengers do that, and it makes sense because a lot of times pictures exchanged via IM are not meant to be stored or printed, just quickly viewed.
I think it would fit nicely in the "upload file" dialog, to add an input box with the JPEG compression factor and a resize resize percentage chooser (dropdown or whatever). I think that since Pillow is already a dependency of gajim, we don't need to an extra dependency.