widgets.statusbar: removed space between size and size unit
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"
Allow to pass custom options to w3mimgdisplay

Can be useful to change image display offset or adapt to term
background color.

See http://w3m.cvs.sourceforge.net/viewvc/w3m/w3m/doc/README.img for
available options.
Image preview: clear images without full redraw