Rearranging make_coords_initial and fixing symmetry bug in auto mesh

[momchil-flex]

• The first structure in the structures list is the simulation, so the center and size can be taken from there - don't need to be passed
• The symmetry on the other hand needs to be passed, because we need to truncate the domain to the symmetry quadrant when we do the auto meshing

[weiliangjin2021]

One possible issue here is the possibility of indsmax=[], which can arise e.g. when looking at mesh at x=0 but there is a structure of zero size along x and placed at x=0. I added the following lines to make it work, but not sure if it's correct,

if len(indsmax)==0:
              continue

[momchil-flex]

I think this cannot happen, because previously we have made sure that only structures that are at least partially in the simulation domain are being meshed. Therefore, the "right" edge of a given structure has to be at least larger than the left edge of the simulation domain, which is the first element in interval_coords.