Add function to set all parameters in a component to free or not free

- component.set_parameters_free:
Sets either all the parameters in a component free, or just the ones
with the same name as supplied in a list.
- component.set_parameters_not_free:
Same as set_parameters_free, but opposite.
Small change to input handling in set_parameter_free/not_free

As suggested by Francisco
Merge branch 'master' into parameter_set_free_unfree
Fix documentation in component.set_parameter_free and set_parameter_not_free
Add functions to set parameters in components in models to free or not
Add test for parameter.set_parameters_free and set_parameters_not_free
Add tests for m.set_parameters_free/not_free
Add documentation for the set_parameter_free/not_free functions

Both for the component and the model version
Added a missing line in set_parameter_free/not_free user-guide documentation
Fix bug in set_parameter_free/not_free user-guide documentation
Several improvments to set_parameter_free/not_free docstrings

They should now "render" correctly for the webpage.
Merge branch 'master' into parameter_set_free_unfree