v0.6.4

• fix #540 WebComponent support: CSS file now insert before grid instead of 'head'
• fix #1143 nested grids with different acceptWidgets class
• fix #1142 add/remove widget will also trigger change events when it should.
• optimized change callback to save original x,y,w,h values and only call those that changed #1148
• delete bower since dead for a while now