Fix bug with ignorePeriodicity

For some meshes with includes periodic nodes listed in the $Periodic section of the msh file, the GmshReader plugin for ParaView crashes. The fix implemented in the branch "ignorePeriodicity" solves the issue.

Basically, periodic nodes are now read AND coordinates of periodic nodes are aligned if the option variable named ignorePeriodicity is set to false. Before this fix, periodic nodes were read independently from this option variable and only the alignement of the periodic nodes was performed based on the value of ignorePeriodicity, which was not consistent.