Throw a helpful exception if a referenced blueprint does not exist

[duncanmcclean]

This pull request adds a helpful exception that'll be thrown if a specified blueprint does not exist. I've added an Ignition solution to the exception that'll suggest any blueprints close ish to the specified one (done the same way as in the CollectionNotFoundException)

Closes #3920

Ignition Exception

[jasonvarga]

Can we call it BlueprintNotFoundException? We use the "not found" pattern all over. You even use it in the message. 😄

[duncanmcclean]

Can we call it BlueprintNotFoundException? We use the "not found" pattern all over. You even use it in the message. 😄

One step ahead of you, see dd72ea2.

[jasonvarga]

I don't know how helpful the suggestions are.

I renamed a blueprint in order to see the error.
Then the exception said Did you mean user? so I changed my entry to blueprint: user

Then I get this, which is probably even more confusing.

If we want to provide suggestions, maybe we should pass in the namespace so it only suggests ones that would work.

[jasonvarga]

It's an easy fix, I'll just do it 👍