[Merge] ~nteodosio/software-properties:xenial-ua into software-properties:ubuntu/xenial

[Nathan Teodosio]

There is still a problem to solve: Ubuntu Pro SVG logo is black: https://people.canonical.com/~npt/update-manager/pro-logo-on-xenial.png.
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https://code.launchpad.net/~nteodosio/software-properties/+git/software-properties/+merge/448388
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