Add the ability to disable remembering playback speed

[xeo]

When we set a different playback speed, we usually do it for one file. For example, I play podcast file (only voice) with 1,10 speed, then I want to switch to music file which is played at a bad speed and have to be reset manually (if noticed).
Add the ability to disable remembering playback speed. In this window something like "Remember setting" option could be added, so it can be enabled or disabled.