ui: Stop abusing position:fixed

This breaks in various ways on iPad, and is not needed anyway.
ui: Simplify sidebar design

We now just display the album list, and handle touch events on the
topmost album correctly (it used to be caught by a stray div).
ui: Prevent vertical scrolling from happening in viewer
ui: Sort the album list after loading it
ui: encode special characters in URL hash

Not doing so seems to break some webkit browsers like Safari (but not
Chrome, which makes me wonder if JavascriptCore is the reason, as
Epiphany breaks too).