cl_maxfps*: various adjustments

cl_maxfps*: various adjustments

Ensures minimum FPS of 10 even while idle to prevent weird issues
(networking assumes at least 10).
If you want to save more resources, hide the game window (disables
rendering entirely) such as by using vid_minimize_on_focus_loss 1.

Disables cl_maxfps_alwayssleep by default, on modern systems with
accurate timers and higher FPS this has a significant impact.

Allows cl_maxfps_alwayssleep to be used with cl_maxfps 0, this was
requested some time ago.

Switches from cl_maxidlefps to cl_maxfps when querying servers to give
pings representative of what can be expected when playing on them.

Cleans up the cl_maxfps* code.

Signed-off-by: bones_was_here <bones_was_here@xonotic.au>