[GRID Builder] add Mass action

[fsoedjede]

Hello!

Thanks for this bundle.
When creating grid from the grid builder using ad GridType (Resources/doc/grid.md), I can't add mass actions in the type.
I've checked and it's not implemented for the GridBuilder
Did someone already did it to push it? I can do it if not and made a pull request if necessary

EDIT: It is possible to add the mass action in the controller. Is it the better way to do it?

Thanks