Add Gamma option to the EQ filter

[isben]

FastFlix 5.12.4

In the Advanced Tab, the Equalizer filter offers Brightness, Contrast and Saturation options.
Actually Gamma is more useful than Brightness since it only affects the mid tones.
There is ample space to squeeze Gamma at the end of the line though, so if you can add it it would be nice, if not replace Brightness please