Added optional reason to the ignore feature.

In multiplayer, this supports players to associate a reason with ignored users that is displayed with the ignored username. Resolves http://wiki.wesnoth.org/EasyCoding#Add_possibility_to_give_reason_for_.22ignore.22.
Better formatting for "planning mode activated" message.
Fix a typo in DiD.

The issue was discovered by vultraz.
More verbose symbol name in translated message.