Allow overriding the blueprint field 'title' required parameter.

I noticed the panel sets the required parameter to true if a field name is set to 'title'. This works fine and is expected for most cases but, in my set up for instance, I have files that have a "title" field and a longer "caption" field.

I don't require a title to be filled out on all my images so this change means we can override the required status for the "title" by setting `required: false` in the blueprint. The other option might be to not require a title field for files specifically.