Editing blogs from the wrong Network Admin

[westi]

#14185 blocked the editing of blogs from the wrong Network Admin but didn't hide the edit links.

We should make this behaviour filterable and use a function to centralise the check in one place that we can then use everywhere.

A extra check slipped in in [16607] where we should also use this function.

[westi]

(In [16765]) Use a span so we mark up the all the info about the site. See #15716 - allows for css targetting based on site.

[nacin]

[16765] looks like invalidly nested HTML.

[westi]

Replying to nacin:

[16765] looks like invalidly nested HTML.

Bah. It worked :-)

[westi]

(In [16962]) Fix HTML validation errors. Fixes #15716.