This patch moves the magnifier rect computation over to the server side
to ensure that the mouse cursor position and the screen image never get
out of sync.
Since applications using Core::EventLoop no longer need to create a
socket in /tmp/rpc/, and also don't need to listen for incoming
connections on this socket, we can remove a whole bunch of pledges!
Instead of having the window non-resizable, it now defaults to a frame
size of 200 x 200 pixels but is user-resizable. The shown screenshot
updates its size accordingly. :^)
Sometimes we might need a larger view, or a non-square shape.
