Within the attribute table, there is a new button to trigger actions
which are not based on individual features but instead on the whole layer.
Normally they will perform actions based on all features or the selection.
In addition to this, a lot of cleanup has been done.
The original name was not representative for the scope of the class
and misleading at best.
The class manages actions for a given layer and it's not a single action
like the former name suggested.
There is a typedef introduced to keep it in the API until we can remove
it with QGIS 3.
