widgets.statusbar: removed space between size and size unit
ext: add img_display

This new file provides functions to draw images in the terminal.
Display image preview using w3mimgdisplay

It works, but is rather hackish.
Add 'preview_images' setting
Merge remote-tracking branch 'potato/img-preview'
fsobject.file: remove is_image(), use existing "image" attribute
widgets.browserview: don't collapse preview when drawing images
widgets.pager: draw the image at the very end
widgets.pager: no unnecessary redrawing of images
gui.ui: shift column levels by 1 when pressing "i"