Added getSource method for DataGridRowView.
Merge pull request #24 from beregond/rowview

Added getSource method for DataGridRowView.
Fixed empty value extension to handle 0 values.
Merge pull request #25 from norzechowicz/fix

Fixed empty value extension to handle 0 values.
Fixed value_format option type
Merge pull request #26 from norzechowicz/dev

Fixed value_format option type
Expanded symfony action column. Added url_attr and content options.
Added expanded example of content and url_attr options usage in action column
Merge pull request #27 from norzechowicz/dev

Expanded symfony action column.