Button: when no label is displayed, set title attribute on icon

[becky]

currently the title attribute is only assigned to buttons if they are created programmatically. Need to update the button code to assign the label from the containerNode to this.label if it doesn't already exist. Then assign title attribute to div containing the icon for the button. However when I implemented this (the title attribute on the div), the browser does not display the title on mouseover so needs more investigation.

[becky]

discussed at July 23, 2007 dijit meeting. Need to add showLabel parameter to button

[becky]

(In [9820]) fixes #3815 added showLabel parameter on button to display text label or not; When showLabel=false add title attribute to button so mouseover browser tooltip is displayed. Update toolbar styles so that label is NOT automatically turned off for buttons in a toolbar - dev must use showLabel=false to turn off label. Updated button templates with new attachPoint to set title: titleNode; updated button template to add waiRole and labelledby property so Window-Eyes screen reader would not speak button label twice. Update button and toolbar test pages for new showlabel parameter.