Changes to reproduce T-wave paper and minor fixes

[bergolho]

Hi Sachetto,

First of all, sorry for the long pull request, as several changes accumulated over the last months with the papers and other works. Here is a brief summary of each one:

1. New ECG function to write the diffusive current. We use this function during the T-wave paper. To implement, I have to include the "output_dir" as an additional parameter to the CALC_ECG macro call.

2. Updated the DTI_MESH_INFO structure for the Oxford meshes.

3. Updated the initial conditions for the "set_common_torord_gksgkrtjca_twave" function used in the T-wave paper.

4. Updated the "main_clip_mesh.c" program to enable clipping sections of a mesh at the same time we recover its associated extra_data into a new ".alg" file.

5. Minor fix in the "ToRORd_Land" cellular model. When the default case was used (without extra_data functions), the index of a current modifier was set to zero instead of one. This resulted in an erroneous increased of the APD. Furthermore, the active tension ("Ta") is now included as an additional state-vector variable, so it can be written using a "save_result" function.

6. Updated the "ToRORd_fkatp_mixed_endo_mid_epi_GKsGKrtjca_adjustment" cellular model for the T-wave paper reproducibility.

7. A version of the Minimal model (Bueno-Orovio 2008) cellular model has been added. The equations are being solved using the Rush-Larsen scheme. The code was implemented by Joao Banhato.

8. Increased the maximum number of characters available for a field in the INI file. When using the MPI batch system inside a cluster enviroment the full path of the resultant folders could surpass the previous limit.

Best regards,
Lucas