Use base_name rather than appended_property_name

This PR is likely to interfere with @WilkAndy 's stuff (so I'm pinging him). I'd like to homogenize the way multiple materials work in the TensorMechanics module. For the bridging with Phase Field I've made a bunch of changes already, for example using the ```DerivativeMaterialInterface```. This works in a more natural way if the user can specify a ```base_name``` for an underlying property (and have the derivative names constructed automatically). I.e. the base_name for a UO2 material could be ```UO2```, yielding material properties such as ```UO2_strain``` and ```dUO2_strain/dc```. I adapted the test files, but for the Cosserat material the appended property name was used to generate a new type of strain. To adapt the input files change ```appended_property_name = _couple``` to ```base_name = coupled```.

@WilkAndy, do you need access to the non-coupled strain properties as well? It looks to me like you could just put the Cosserat stress into ```_stress``` rather than in ```_stress_coupled```.

This addresses #4300.