Roster and window size get mixed up

[steve-e]

Guess one wants to try out the different 'Window behavior' modes in preferences and is only switching from one mode to another without changing window geometry by hand.

When you return to your initial option the roster/chat geometry has changed and isn't the same anymore, as it was before you played around with the option.

[asterix]

it's because of the one window for roster + messages mode. What about saving roster width only in this mode (height will keep the value of the mode we used previously). This width is the width of the treeview, not the whole window with messages.

Then in message_window size we put the size of the messages notebook (width and height)

And when we resize the whole window, put take width of roster + width of message, and height of message.

What do you think?

[nicfit]

(In [ac4cab9dc2f92a20f0134d3048d7c6839a16eb11]) More sizing fixes. Along with [a70a5a1f7c0bc65be1fe26b6185bf27531ec5685] closes #3713