Add GR models at multi time steps

Thanks to the PhD of Andrea Ficchi (https://webgr.irstea.fr/wp-content/uploads/2017/09/2017-Thesis_final_Andrea_Ficchi_Irstea_2017.pdf), we now have GR models working at multiple time steps (infra-hourly).

We plan to include some of these models in airGR. Namely, the GR5 model with an interception store seems to be the best candidate for this.

See the Table 5.11 page 210 of the manuscript for results analysis. Indeed, the GR5 model with interception (GR5-I2-FL in the table) provides (at the hourly time step) better results for KGE, high flows and low flows than the classical GR4H model (GR4), than the GR4H model with interception (GR4-I2) and also to a tested GR5H model without interception (GR5-FL).

Another added value to this GR5 model with interception working at diverse time steps is that the consistency of the parameter values between the time steps is improved.