GUI frame rate moved to advanced settings

This allow to keep cpu cool on low powered systems. Old value of 100 fps are kept as default.

I found value of 20 fps to keep my RPI at 700MHz at ~80-85% cpu time. With original value of 100 fps it can produce only 35-38 frames at 1000MHz with 100% cpu time. 20 fps looks pretty good and does not cause any visual defects.

100 fps is unusually high for regular x86 HTPC too.