SQLite for roster is an overkill

Restore RosterListModel and RosterListItem. Break the widget code, I'm
sick and tired of manually editing the sis file. Don't use sqlRoster and
sqlChats - replaced with ListModel and QStringList. Restore MsgItemModel
and MsgListModel because I have a briliant idea. Implement new chats
switcher. Still need to remove lots of stuff related to SQL version of
roster.