Adds a much-requested a way for protocols to give a hint to Kopete which form a chat should take. This allows Kopete to give a chatwindow a size and members list visibility appropriate to the chat.

We've previously told users who requested this feature that it was not possible for consistency's sake, but I feel that this has handicapped our use of chatrooms/IRC in kopete. This solves this dilemma elegantly.

* Form is an attribute of Kopete::ChatSession
* 2 forms of chat: Small and Chatroom
* this affects the initial format of the chatwindow
* Small windows and Chatroom windows layout and members list visibility changes by the user are sticky and persisted independently

Additionally, the feature allows (optionally) a compact variant of the chat view style to be selected dependent on chat session form. This is implemented by munging the relative path to the variant css.

FunkyStyle.css -> _compact_FunkyStyle.css. The rationale for this is that a large style with avatars is not appropriate to a high traffic channel. This allows a compact variant to the main style, but that keeps has consistent theming, and works within the Adium chat spec

Notes on the patch:
* Everything defaults to the current Small behaviour! Even if applied as is, the patch is fail-safe!
* ...Except testbed, for testing and demonstration. This requests Chatroom style windows.

Patch reviewed by Duncan and Boiko