add support for custom boolean column

[abenhamdine]

In one application, we use a custom ux boolean column which modifies tdCls to display fontawesome icons for boolean values :

defaultRenderer: function(value, metaData) {

			var customCls = '';
			var ret = '';

			if (value === true) {
				customCls = 'arh-grid-col-boolean-td-true';
				ret = this.trueText;
			} else if (value === false) {
				customCls = 'arh-grid-col-boolean-td-false';
				if (this.arhDisplayGlyphForFalseValue) {
					ret = this.falseText;
				} else {
					ret = '';
				}
			} else {
				if (this.arhDistinctNull) {
					customCls = 'arh-grid-col-boolean-td-null';
					ret = this.undefinedText;
				} else {
					customCls = 'arh-grid-col-boolean-td-false';
					if (this.arhDisplayGlyphForFalseValue) {
						ret = this.falseText;
					} else {
						ret = '';
					}
				}
			}

			metaData.tdCls = customCls;

			return ret;

		}

currently nothing is displayed in print view :
grid :

print preview :

[abenhamdine]

add a helper getHtmlForPrint() in grid column ?
other possible name : printRenderer()