Add facility to edit nicknames / remove nickname entry

This allows users to edit one or more nick name entries in a single
session. Entries can also be removed individually.

Based on mock up by Lubomir Ivanov and various conversations from Dirk.
Thanks to both.

[Dirk Hohndel: quite a bit of editing for coding style and whitespace]

Signed-off-by: Amit Chaudhuri <amit.k.chaudhuri@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>