Improve animations

This does a few things:

* Replaces the start screen JS animation with a css animation.
* Speeds up the start screen animation (it used to take 30 seconds, now it takes 3).
* Rejigs cloud management, so that the same 8 clouds are used in an infinitely looped CSS animation. Previously, clouds were created and destroyed when they reached the right of the screen; and the animation was done via CSS transitions. This needed more code to manage.
* Fixes an issue where the sheet on the washing line was not aligned correctly (partly as a result of me changing how the animations worked).
* Partly fixes an issue which occurred while I was testing, where the screen didn't resize to fit the Crosswalk window correctly, by using setTimeout() to call the scale() function.

The animations are smoother on Crosswalk (Android and Tizen) than they were, though they are better on Tizen than Android. Tizen wrt is about as good as Android (i.e. worse than Tizen Crosswalk).

Fixes #8