[Merge] lp:~albaguirre/qtubuntu/use-mir-surface-apis into lp:qtubuntu

[Alberto Aguirre]

@Daniel, I would suggest using mir_demo_server instead as that has the window management rules that are in mir core.

We consider mir_proving_server experimental. 
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https://code.launchpad.net/~albaguirre/qtubuntu/use-mir-surface-apis/+merge/267228
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