Add EIM algorithm minor fixes

[Steriva]

This pull request adds the EIM algorithm to the offline phase to place sensors, then some minor fixes and some small new features have been implemented:

• POD has now test error within the offline subpackage
• Add a check on the guess parameter for the PE
• Adding the possibility of performing repeated experiments for TR_GEIM to gain statistics
• Automation of the check_input for norms
• Minor fix in write_read for OF