Add uploadFromUrl and restructure other upload methods (fixes #70)

[Xymph]

See #70. Previously, upload() took $data and uploadFile() invoked upload(). However, uploadFromUrl() takes $url and otherwise needs exactly the same code as upload(). To allow sharing this common code, I had to restructure upload() a bit into a private method, uploadCommon() (maybe there's a better name for that?), and then its public use is made clearer by a new name, uploadData().

The previous merge is just a few days old (so hasn't spread far yet) and still falls under "current development", so this API change seems acceptable to me, as it leads to consistent naming of the three public upload methods. For further consistency, I renamed download() to downloadData() as well.

[Xymph]

Minor code change in addition to the restructuring of 4899d33: is_null($text) is a better way to test input parameters than === null.

Also note that upload from URL goes through the same multipart POST in Wikimate, even though this isn't needed when the request contains no binary data -- but it doesn't hurt to do it that way either.

[Xymph]

@waldyrious, would you be able to squeeze in a review one of these days? 😉

[waldyrious]

Shouldn't either this line use "relevant ... properties", or line 529 use "all ... properties"? For consistency.

[Xymph]

Well, it gets far more properties than for a page, and I meant it more in the sense of "list all those that are to be retrieved, and don't list those that won't be retrieved". :) But 'relevant' is fine too.

Either way, 'image' should be 'file', so thanks for highlighting this anyway.

[waldyrious]

Apart from the minor comments I've left inline, this LGTM :)

[waldyrious]

@waldyrious, would you be able to squeeze in a review one of these days? 😉

Oh, crap, you were faster :P I had this page open for the last few days and didn't refresh it before starting the review, so I hadn't seen this comment when I started. I'm saying this just to reassure you that I didn't review the PR now following your prompt, but indeed hadn't forgotten :)

[Xymph]

Sorry. 😉 I guess all the quick review turnarounds in the past spoiled me a bit, but I thought I'd poll you after 5 days.
Thanks again, time to wrap up this one.