Fix some minor CSS issues
Make formatter for CheckboxSelection an argument
Make formatter for CheckboxSelection an argument
Minor css issues
Minor css issues
Minor css issues
Squashed commit of the following:

commit 6ea4aa598fdab63b1058b087581ae7e9dfaa6f9b
Author: zoechi <gzoechi@gmail.com>
Date:   Tue Sep 9 17:19:53 2014 +0200

    bwu_datagrid-95 Group total shows the same sum value in each group totals row
    fixes #95
Conflicts:
	lib/dataview/aggregators.dart
	lib/dataview/dataview.dart
bwu_datagrid-95 Group total shows the same sum value in each group totals row