GRIM/EMI: Stop frame time while debugger is open.
EMI/GRIM: Handle normal mode and draw mode in separate virtual methods.
EMI: Improve pause handling

Both EMI and Grim call RenderModeUser when entering the menus or dialogs,
but EMI does not use special "blast" commands to display text or images,
so we cannot suspend regular screen updates. The current implementation
does not switch engine modes in RenderModeUser, which has the drawback
that the frame time is not stopped during pause or menu.

With this patch, EMI handles draw mode like normal mode with frozen frame
time.
Merge pull request #775 from inguin/emi-pause

EMI: Improve pause handling