(bug 58376) white space in topic title appears in 'Comment on " title"' placeholder

When submitting a new topic, title text was already trimmed; this will also trim
title text when edited & do another trim before displaying it.

Mingle: 615
Bug: 58376
Change-Id: Ie4798cd3069cfaf0a81cc786fae4b984af235cf9
Merge "(bug 58376) white space in topic title appears in 'Comment on " title"' placeholder"