maxverticies higher default and auto detection(?)

[gak]

maxvertices is quite low for todays standards, so it would be good to have a higher default and potentially (somehow) detect what is a good number for the hardware.

Potentially:

1. detect a drop in the redering framerate to automatically lower the maxverticies
2. By default, don't lower the tailskip variable, but decrease the tail length accordingly (since it will be a more seamless experience to the user and still look good)

[FrMo]

1. could be done with some timing code in or around drawAll(); possibly excluding drawOSD() and conDraw() from the measurement. We need a rule of thumb to decide on using less vertices, for example: if drawing time is more than a certain threshold ( 40ms = 25FPS), decrease maxvertices by 20%. Maybe gravit should wait until several frames have hit this threshold, to avoid "false alarms" caused by the OS (scheduling, swapping, etc).

2. seems to be a good strategy

[FrMo]

there is a similar problem with the fill rate for particles sprites: with too many big particle sprites drawn onto the sceen, the framerate drops dramaticially; this can be cured by reducing particleSizeMax.