Add photoset_layout as an option to create_photo

[taylanpince]

Even though this is not a documented feature of the Tumblr API, it works well, and this attribute is actually provided by their Posts endpoint (http://www.tumblr.com/docs/en/api/v2#posts)

Allowing this photoset_layout option as a valid attribute to create an image post would be a nice addition since it gives full control over how photos are laid out in the template.

[taylanpince]

I just noticed that my other other commit also sneaked in here. To explain: I noticed that if I provide an empty tags list, Tumblr API responds with an Authentication error. Probably an issue related to the way the request is signed. I added a sanity check to prevent this issue, it was quite puzzling.

[codingjester]

Good call on the tag list. Can you do me a favor and add a test for this to make sure the web request doesn't send the empty tag list? Once you have that, I think we're ok to pull you in.

[alikaragoz]

Thanks @taylanpince very useful 👍

[taylanpince]

@codingjester For sure, I'll handle this over the weekend.
@alikaragoz Thanks!

[jasonpenny]

I know this pull request is very old, but we will need a signed CLA to pull this in

[yahoocla]

Thank you for submitting this pull request, however I do not see a valid CLA on file for you. Before we can merge this request please visit https://yahoocla.herokuapp.com/ and agree to the terms. Thanks! 😄

[taylanpince]

@jasonpenny I don't even remember opening this PR, but sure, I signed the CLA 😄

[jasonpenny]

haha, thanks!