Added custom classes to column definitions

Added data-hdr-class and data-row-class properties to column definition.
data-hdr-class will be added to TH cell's class attribute while
data-row-class will be added to each TD cell's class attribute belonging
to the column.

E.g.: <th ... data-hdr-class="hidden-xs hidden-sm"
data-row-class="hidden-xs hidden-sm">
The code above will hide the column in small devices.