send only allowed file types to iThenticate

[forgive38]

Hello

I propose this PR in order to restrict the number of files sent to iThenticate, based on iThenticate allowed file types.

I hope that helps,
Thank you

[asmecher]

@forgive38, just curious -- what happens when an unsupported file type is uploaded to the iThenticate service?

[forgive38]

@asmecher : there is an error when you schedule the detection

For example, screenshot for the file J.png

And since all files of a new submission are automatically sent to iThenticate, that adds an extra delay: it impacts the ui experience (sending files to iThenticate is synchronous, maybe it can be asynchronous via a Job ? - I will make an issue)

[touhidurabir]

maybe it can be asynchronous via a Job

@forgive38 I think thats a good idea. but as that going to some good amount of enhancement(probably), I may suggest to go for such major change in 3.5+ compatible only . But a separate issue is a good place to discuss about that .