Add hook before and after delete a file

[SamyLegal]

Add possibility, for the localfile field, of specify a pre and/or post hook when we delete a file.

When i upload an image on my website with the localfile field, i generate multiple images of differents size. For that, i use post move hook of localfile. I have add a pre/post delete hook to delete images i have generate, when i delete the original file.

[grabbou]

Hi @SamyLegal , thanks for your PR!

It's a nice feature to add to our 'before-React' releases as hooks will come out of the box with our next major release. I left my private comments on lines you've made (especially due to code-style guide we have here.

I am a huge fun of being consistent so that's why I'd feel more enthusiastic about that if all of our fields have the same list of hooks available but we are going to change that mechanism anyway in the nearest future.

Let's wait for the others (especially for @JedWatson) and see what we can do.

[SamyLegal]

Hi,

Thank you for the answer.

I'm agree with you for use dot notation instead bracket notation.
I have used bracket notation because 'delete' is a reserved word in javascript (jshint give me an error) and i have used this word because you use it in your code.
I can use another word like 'remove' or if you prefer i can remove quotes too, tell-me.

Otherwise, i have add comments.

Thanks.

[morenoh149]

this could be useful

[creynders]

Hi @SamyLegal sorry for the very long wait. Just a quick update: I've rewritten the entire hooking mechanism for keystone, which will land in v0.4. This means that your PR would need a number of changes to be up-to-date. We're starting assembly of v0.4 changes today or tomorrow, so I'm going to take this PR along partially and modify it to use the new hooking system.

[JedWatson]

Closing in line with @creynders note - this has been superseded. Thanks for the original PR @SamyLegal!