Various EogThumbView bugfixes

new feature b002458d : This commit permit to control the monitors. I'm working on a plugin eog-plugin-images-manager where I have virtual folders and I need to deactivate the monitors to avoid displaying some images I don't want to.

Fix bug ae27263e : I found that if in Eog you open a folder with the flag --single-window and in another terminal you open another folder with the same numbers of images, the jobs doesn't load this thumbnails. It's because in the file eog-thumb-view.c they are a condition where you check if the old range is equal to the new you return.