Allow empty strings as config values.

[xim]

The way you assign default values to config does not permit empty string: quickWidth = conf.qtWidth || '500px';

E.g. if I set config.qtWidth = ''; I still get the value 500px as the default width.

config.qtWidth === undefined ? '500px' : config.qtWidth would allow empty border, width, etc.

As a workaround, I am using

config.qtBorder = [];
config.qtWidth = [];

This, however, adds an ugly and strange border to the preview and a border="" to the HTML. Would prefer to just add config.qtBorder = '';