Validate script creation

[johrstrom]

We've noticed this case where

1. You create a project from a directory that does not exist
   • there's no validation, it lets you do this
2. You try to create a 'job setting' (script) but you cannot.

You cannot create a new job setting because you cannot choose an appropriate file to render because the project directory was invalid when you created it. The file list is populated by /scenes//[.ma|.mb].

As a user it's not apparent what's gone wrong, because it went wrong on the previous step, not this one.

It's not apparent that you can't create a new job setting (script) because you're project is bad, so let's put a check in place to ensure only valid projects get created. Valid by this standard being that it has 1 or more scene files in it's scene subdirectory.

[johrstrom]

I made a couple commits to this so at least when a user does get into this situation they should be aware of it. One bit is it won't submit if the file to render doesn't actually exist.

[johrstrom]

Changing this to validate script creation because we now have test cases for project. This ticket will solely fix creating job settings.