Auto-distribution of unstructured grid read from a file.
+ Unstructured grid read from a file is now distributed automatically among clients if there is
no distribution information provided.
+ Attributes of grid can be setup: From model (highest priority), from file (reading), or auto-generation (lowest priority).
If an attribute can be setup by several ways, it will be setup by one with the higher priority.
Test
+ On Curie
+ Tests pass