add new module CheckBoxColumn.js

This is very useful module for create check box column by store value.

check box column can dynamic show and hide by API.
check box column can dynamic disable and enable by API.
check box column can sort by check box store value.
0: unCheck
1: partial
2: checked
 
you can use like:
```javascript
  var struct =  [
             {id: "checkBox", name: "", field: "checkBox", width:"18px" },
             {id: "group", name: "Group", field: "group", width:"240px"}
         ];

  var store = new Memory({
       data: [
          { id: 0, group: 'Administrator', checkBox: 0},
          { id: 11, group: 'hurry', checkBox: 0},
          { id: 111, group: 'X', checkBox: 0},
          { id: 21, group: 'XL',  checkBox: 0},
          { id: 31, group: 'XXL', checkBox: 0}
       ]
   });

  var grid = new Grid({
                        id: "grid",
                        cacheClass: Cache,
                        pageSize: 40,
                        store: store,
                        autoWidth: true,
                        structure: struct,
                        modules: [
                                SingleSort,
                                HiddenColumns,
                                CheckBoxColumn
                        ]
                });
   grid.placeAt("gridxDiv");
   grid.startup();
```

![checkboxcolumn](https://cloud.githubusercontent.com/assets/4166657/2753031/a0362138-c926-11e3-909c-f20a9116849e.png)