Allow PybammBuilder to remove/add costs, datasets, models

[BradyPlanden]

Allow the pybamm builder to remove costs and reapply new costs alongside resetting the model and dataset would be helpful in reducing the verbosity of the multi-fitting style problems. Here's the syntax I'm thinking of:

# First build
builder = pybop.builders.Pybamm()
builder.set_dataset(dataset)
builder.set_simulation(model_1)
builder.add_parameter("Positive electrode active material volume fraction", initial_value=0.6)
builder.add_cost(pybop.costs.pybamm.SumSquaredError("Voltage [V]", "Voltage [V]", 1.0))
builder.set_experiment(experiment)
problem = builder.build()

# Remove all costs, add a new one and build
builder.remove_costs()
builder.add_cost(pybop.costs.pybamm.RootMeanSquaredError("Voltage [V]", "Voltage [V]", 1.0))
problem2 = builder.build()

# Set a new model and build
builder.set_model(model_2)
problem3 = builder.build()

# Set new dataset and build
builder.set_dataset(dataset_2)
problem4 = builder.build()