Issue: 🐛Bug report | Image library does not check for file extension and will fail without clear error messages

[stevenlabelle]

Description: When images are loaded with FERawImage::Load there is no check that the user entered the file extension type which will cause the program to terminate with the message "Model initialization failed".
E.g., when using FEBioWarp, if the user sets a target image to a raw file but does not include ".raw" in the name then FEBio will fail to initialize the constraint. The log error outputs are: "Nonlinear constraint 1 failed to initialize" and "Model initialization failed".

Version: Dev version 4.9.0.7d6f0796f

To reproduce:

1. Create a model that uses image data (e.g., test1_v4.feb from the warp plugin).
2. Remove ".raw" from the file name in the file field.
3. Run FEBio. The model will fail without.