Supply a reload feature for static ro-windows

[Andreas Wehler]

zim 0.60; Ubuntu 14.04

You can always start a "New window" of some page, which is rendered as is
in read-only mode and may be placed for reference and look-up, or even
for copy/paste of contents.

In case the content was changed regularly the static ro-window is not
refreshed. It would be very helpful if some hot key (e.g. Ctrl-R) would
allow such a window to be refreshed, or even refresh automatically
when getting focus.

Thanks,

   Andreas