Version ap: a lot less jittery

No new features, only fixes for bugs. From most to least embarrassing:

* If you selected some text and then hit the 'clear' button the app would crash.

* Dragging the mouse/finger around on top of the settings menu (without touching sliders) was selecting text underneath the settings menu. I've hopefully fixed all such problems now.

* Settings were only saved across restart if you tapped on the 'settings' button to close the settings menu (rather than tapping anywhere outside the settings menu to close it). Now settings should save across restart once the menu closes.

* The overflow button would sometimes unnecessarily be introduced when there was enough space for the final button.

* If you hit 'save' you got no feedback on whether things had been saved or you'd fat fingered some other button. Now buttons flash to white when you tap them.

* Small phone screens turn out to be quite sensitive. Taps often triggered double events (like performing a button action and then selecting some text on the editor behind it). Now there's some hysteresis; after a touch, further touches are ignored for a brief (sub-second) period.

* Tapping the 'paste' button could not be undone. It's not very discoverable because it's often inaccessible on mobile devices, but the editor in Lua Carousel supports undo (`ctrl+z`) and redo (`ctrl+y`). While we were able to undo paste after `ctrl+v`, undo wouldn't work after tapping the 'paste' button. Now it should work if you can get to it.

* Tapping the cursor within the editor would cause a brief distracting flash. No longer. Many thanks to Llamamoe on Hacker News for pointing out this problem that I was completely blind to.