[py] Add WPEWebKit driver

[carlosgcampos]

For the WPE port of WebKit

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[lmtierney]

Are we going to keep adding lesser-used webdrivers to the selenium code base? A quick look at the code looks like you could easily just subclass the WebKitGTK Options and pass it directly to the WebKitGTK webdriver.

[carlosgcampos]

Well, WPE is not used for general purpose desktop browsers, but it's used in a lot of embedded devices. The driver is similar to the WebKitGTK+ one, but all driver impls are quite similar to each other. Problem of subclassing is that options of WebKitGTK+ might not make sense in WPE (and the other way around). like for example the overlay scrollbars option. Anyway, I don't plan to add more drivers :-)

[aperezdc]

Ping. Any chance of having this merged?

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