Modify struct CNMF_results

[degleris1]

Several function take CNMF_results as an argument, including important visualization tools.

However, if the user has a W and H from some other algorithm, they must put in the CNMF_results struct first and set a number of parameters to nothing. I propose we either (a) overload these functions with their corresponding non-struct arguments or (b) change the last fields of the struct (l1_reg, l2_reg, ...) to a single field model_params which contains a dictionary.

[bantin]

@degleris1 I think adding methods to the visualization function is a good way to address this.