Click a column header to sort issues list requires annoyingly accurate mouse aim (BB-16051)

Steps to reproduce:

• Browse an issue list
• Click a column header, such as "Title" anywhere other than the word "Title" itself, e.g. in the large empty space, or on the arrow.
• Nothing happens.

This is not straightforward UX, because there is no visual indicator that clicking on the text itself will do anything differently than clicking anywhere else in the header. For example, if you made the header title underline on mouseover, then it would give a visual cue to the user that "oh, I have to click on the word itself."

In fact, the only mouseover-related visual cue we are given is that an arrow appears when you mouseover anywhere on the header, which would seem to indicate that clicking anywhere on the header will do something.

Proposed remedy:

• Allow clicking anywhere in the header to affect the same change as clicking directly on the title of the header.