Allow Manually Adjust Mark Line

[Nathan Handler]

Lernid currently attempts to draw a horizontal line in the #ubuntu-classroom-chat channel to help users keep track of where they left off reading. This would be a lot more useful if the user could manually control the line. For instance, in irssi, I can hit Alt+m to move the line below the last message in the channel. Adding a second line in #ubuntu-classroom would also be helpful. Maybe allow the user to drag and drop the line with the mouse as well.