Make it possible to freeze a slide.

At the moment, if you want to move down two verses you can either work out which verse number you are interested in, and press `v3`, etc. Alternatively you can use a mouse to click the required verse. A third option is to `Blank to Theme`, press the down arrow twice, then unblank. However, this is disruptive.

I propose an option similar to "Blank to Theme" which simply freezes the current slide until deactivated. This would enable you to move down two slides simply by pressing the keyboard shortcut for "freeze slide", then clicking the down arrow twice, and unfreezing the slide.

This is similar to Media Shout's default mode, except Media Shout is always in "Freeze Slide" mode, and down arrows never display the current slide, unless you press "Enter".