Param interpolation

This branch partially implements the ability of store default interpolation for individual parameters. The static option has been changed to be stored in the parameter itself instead on the layer. 

When a constant (sub)parameter is modified in animated mode, this is the sequence of decisions taken to add the waypoint:

1) If the parameter is static do not produce any waypoint just modify the (sub)parameter value and keep it constant
2) Else if the parameter is not static then look up its interpolation property. 
3) If it is set to "NONE" then use the interpolation from the toolbox defaults.
4) Else if it is set to any other interpolation type then the waypoint created will use that interpolation.

This feature is not complete at the moment because there are layers pending to implement, but the merge request is being sent because it gets more complicated each time to rebase the branch onto master (what is growing up).

The functionality of the layers and its parameters that are not migrated to this behavior is preserved to be as the old way and doesn't interfere on the program usage.