Low FPS With Transmatter Terminal

[Siombre]

The Transmatter Terminal causes low FPS when it is open and there are many types of item in the system.
This low FPS goes away when a filter is applied that drastically reduces the number of items being shown.

I think that this is caused by the terminal grid not having a cap on the number of items it displays, even if those items would be cut off by the bottom of the window.

I think this could be solved by limiting shownItems to grid.columns*10 items near the end of the terminal's refreshDisplay function, or by otherwise changing the grid display to only attempt to draw onscreen items.