Force and moment partitioning influence potential solver 2D

- Fixed a bug where using a single output argument causes a formatting error.

- Extended the influence field to multi-body configurations.
- Added an output argument for surface normal vectors on the reference geometry.
- Optimized the organization of the input and output arguments accordingly.
- Updates in the headlines.

- Optimized the outer boundary detection to prevent potential false boundary conditions.
- Changed the default minimum triangular size to 0.5*innerTrSize to prevent potential insufficient element size.

- Added output options including phi values on the body surface and the corresponding x- and y- gradients.