Add findOrFail

[francoism90]

Laravel offers Model::findOrFail(..), this is really useful as you don't need to write logic for it when the value is null.

Would you consider adding it? I'll try to create a PR, but would like to know if this feature is wanted first. :)

[riasvdv]

Sure! You can call it findByPrefixedIdOrFail to keep it in line with the naming

[francoism90]

@riasvdv See #11 , hopefully it's Ok, please let me know if any changes are needed. :)