Differential Action Models -- abstraction and clean up

I started by creating a very simple abstraction for it. These also included the follows:

• documentation for this abstract class,
• a fixed bug in the DAMLQR.

Despite this method is enough for DAM model, it doesn't apply to DAM data; and I would like to create an abstraction to this class too (avoiding user errors). Checking the code I found the follows:

1. Some DAM data classes require the costModel to allocate data.
2. I would expect that for dynamic data (e.g. Fx) we will follow pattern (1).
3. The CostSum class can be used only for Pinocchio cases. Then we can't follow pattern (1) for all cases.
4. nu depends on the actuation model, then I could use it for constructing DAM model classes.

One way of tackling this issue might be, for instance, by constructing a DAM model/data given a dynamicsModel and costModel. If we want to do it, we need to do the follows:

1. Create a dynamicModel abstraction which allocates dynamic datas as costModel.
2. Create a dynamicModelPinocchio which also includes Pinocchio model and contact model.
3. Create a costModel abstraction

For the time being, I used costData inside the abstract class for DAM data. I believe this mightn't the best way of doing it