Speed up start animation

Initial fix to make working on the app easier. Made the start
animation ~10 times faster.
Replace js animation with css one
Replace cloud animation with css animations rather than transitions

These have the benefit of being infitely loopable, removing
the need to add/remove clouds when they reach the right-hand edge
and all the associated event handling.

They are also easier to set up, as we don't have to wait for the
element to be in the DOM to apply the animation.

However, this does mean that the same set of clouds continually
floats across the background, unlike the old approach. But because
the animation durations are randomised, there's still enough
change for it to continue to look interesting.
wind_wave_sheet animation already applies translateX

Remove the double translateX() (once in the element rule, once in
the animation). NB this fixes an issue where the sheet was
displaced to the right by about 50%.
Really fix the sheet's positioning

I ended up adding another container to position the sheet
in the centre of the washing line; then I position the sheet to
that. (There seemed to be some issue where translateX(-50%)
wasn't being assigned correctly when combined with skew.)
Add small delay to make animation appear smoother

This slightly improves the feel of the initial startup animation.
Wait before resizing to get better measurements

I noticed some issues with the app failing to fill the window
on Android, when it was rotated and it resized itself.

By putting some setTimeout() calls around the scale() function,
we should be able to get more accurate measurements, which should
reduce occurrences of this.

However, I still haven't been able to completely get rid of
these resizing artefacts.
Merge pull request #16 from 01org/improve-animations-8

Improve animations