[Merge] lp:~kai-mast/friends/links into lp:friends

[Kai Mast]

Better? 

I am not sure how to use just one linkify function because some have absolute addresses and some don't, so I now have linkify and linkify_mention, where the latter calls the first.

I also made the links use https which should be used whenever possible in my opinion.
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https://code.launchpad.net/~kai-mast/friends/links/+merge/202954
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