print window is too small in chromium

[maxnikulin]

In chromium (linux) the window opened by support/printer.js is too small,
so just "Save" button is visible. It is necessary to resize the window
to get over controls visible.

If empty string is passed instead of long list of options in https://github.com/oria/gridx/blob/master/support/printer.js#L90 then

1. a new tab is opened instead of new window
2. there are a set of controls and a preview frame in that tab
   so it looks nicer than a bit strange small window
   generated by the current code.

The issue may be reproduced with tests/test_grid_printer.html file. Just click "Print"