potential bug with bindings

[HorvathDawson]

Hey @diegoferigo

I am not sure if this causes issues but I realised it while working on my own bindings for my backend.

Here you do not have a template for a vector of modelptrs. I believe this would cause a memory leak in swig when you call (world obj).models().

[HorvathDawson]

Also would it be possible to move this the include "to_gazebo" to instead be at the top of the gazebo.i file here ?

This way if core.i is exposed downstream it would avoid needing to exposure gazebo.i too