Custom URL: wrong mapping in issue context (BB-6167)

• Links to user accounts (here: authors of issue comments) use the custom URL as well, while they should be using bitbucket.org (like on Overview page).
• When embedding changeset links via the toolbar, the custom URL gets used. That's ok, but it must not include the user/account name in that case since it's already part of the custom URL.

Cheers