System messages related to contacts

[sander]

This is an entry containing 3 related requests:

1) System messages related to contacts (like presence and nickname changes) should be be remembered for the current session only. It makes no sense to remember them for future Coccinella sessions in chat history. This is only a privacy issue.

2) In the chat dialog there should be a button at the bottom of the dialog to show/hide system messages. (see also http://bugs.kde.org/show_bug.cgi?id=86624 )

3) System messages of a contact should be remembered for the current session even when the chat dialog with the contact is closed. When the user opens the dialog, he should not miss any system message related to this contact since the user was online.

[sander (s-devrieze)]

Related: http://coccinella.im/node/238

[Mats (matsben)]

 * Added config to not display presence changes in history for chats.
 * Added checkbutton to hide system messages in groupchats.

Chat.tcl:
    # Shall we display presence changes in history?
    set ::config(chat,hist-presence) 0
All xml is saved to history file since I want to be complete.
GroupChat.tcl:
There is now a checkbutton (toggle) with an "M" for no good reason, that toggles all system messages, or at least the presence changes in display.

[Mats (matsben)]

Now also added same toggle button to Chat dialog.
Added tooltip for both dialogs.