Basic UI: Clarify "advanced encoder settings" text

Change checkbox with text "Advanced Encoder Settings" to "Use Advanced
Encoder Settings".  This way it will hint that the settings will be
disabled when unchecked.
Basic UI: Remove "CPU" from "x264 CPU Preset" text

I feel like people keep mistaking how x264 preset functions.  They often
associate it with their own CPU speed, and I feel the name does not help
with that issue.  I think it may be for the best to just take it out.
At best, it will keep people away from using it unless they know what
they're doing, and at worst, people at least won't be able to associate
it with their CPU as easily anymore.
Basic UI: Add "Use Constant Bitrate" advanced option.

It's better to use VBR for local recordings, so this option should be
nice for people who want to do that.