Implement parallel input of data files in example

[pierrepebay]

Have 4 ranks reading their own part of data input and have 1 rank generating the image.

[pierrepebay]

When trying to get a rank that doesn't exist in an info object, the exception could be outputted in a more explicit and understandable way.

• Current error:
• Possible better handling: Exception in unordered_map::at : key not found : rank 2 does not exist in this info