Fps drop when viewing energy network or production overview

[rapus]

@performance-devs
at medium zoom in a normal factory i have 59-60 fps but once i open the energy network overview by clicking any pole i drops to slightly above 40 fps
my laptop also begins to slightly decrease its fps to 50-53 when least zoomed in (far away, depending on where i stand, in factory <-> wildness).
the general rule for me seems to be a 20fps drop from normal when i have the energy window open.
seems like that plotting could be enhanced a lot
the production window in turn decreases the fps by even 40.
(60->20 when opening the production window)

[Rseding91]

The "plotting" is just a bunch of lines that get re-drawn each frame. I've done some small optimizations around that GUI for 0.15 but it's simply an intense GUI that takes some CPU time to setup to render each frame.