allow client side shadow windows to be resized

[totaam]

At present, we don't allow them to be resized because we do not want to / cannot resize the whole remote desktop.

However, for this particular case only (not for regular remote application windows) we could add scrollbars when the window ends up being smaller than the remote desktop.

This is particularly useful when accessing a large remote desktop on a small screen (ie: laptop).

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Difficulties:

• add a --max-size option to limit the maximum window size #263: because of a bug in GTK2, we cannot set the maximum size of the window on win32, so we will have to fill the edges with some padding on win32 (other platforms can just limit the window size)
• all mouse events (clicks and motion) will have to be adjusted before sending (easy)
• probably more I can't think of (usually)

[totaam]

Move to 0.16 which has other shadow improvements scheduled.

See also: #976 / #972.

[totaam]

See also #1557, #1567, #2458

[totaam]

The scrollbars could be added for any window bigger than the client's display / monitor.

See also #2455

[totaam]

Could also be used for any fixed-size windows that are too big for the client?