Find a way to use homogenize parsing of models between SDF/URDF/MJCF

[MegMll]

Currently, Pinocchio supports multiple model formats such as URDF, SDF, and MJCF.

However, there is a lack of homogeneity in how these formats are parsed and handled.

Maybe we can try to think of a way to have some homogeneity in the way all these formats and future formats are parsed as pinocchio models, to avoid having a lot of overloaded buildModel functions.

[jorisv]

We must provide an homogeneous API to read each format.

• Some don't have argument in the same orders
• There is many arguments
• There is many version of the same function to avoid breaking the API.
  It's even worst in Python.
  We can maybe use the builder pattern to provide an API that can evolve without breaking the API and that manage lot of optional arguments.

We must fix mjcf::buildModel and mjcf::buildModelFromXML that all read from a filename.