[Merge] lp:~abreu-alexandre/webbrowser-app/theme-color-meta-detection into lp:webbrowser-app

[Alberto Mardegan]

Review: Approve

Since the tests are there, the description needs an update.

The code is good, I just wonder if we should implement some tricks on the text colour, to ensure that it's always visible against the background.
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https://code.launchpad.net/~abreu-alexandre/webbrowser-app/theme-color-meta-detection/+merge/279120
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