Add auto value to possible fill modes of a TimingInput
Rebased existing tests onto new default fill behaviour
Make expectations more clear in source file
Replace container ids with the direction they represent
Ensure the longest string can fit in the test div
Removed hand coded incrementing IDs
Make tested fill value explicit in source HTML
Remove the need to duplicate anim divs for dur 0 and dur 1 by hand
Make direction more clear in source HTML
Add fill mode auto to existing fill test
Added test for fill mode auto on Animations and Timing Groups
Merge pull request #562 from alancutter/fillAuto

HIGH IMPACT BEHAVIOUR CHANGE: Default fill mode auto

This change add support for fill mode auto and makes it the default value for all timing inputs.
For Animations this changes the effective default fill mode from 'forwards' to 'none'.
Animations by default no longer apply their effect outside of their active interval, this matches the existing CSS keyframe animation fill behaviour: http://dev.w3.org/csswg/css-animations/#animation-fill-mode-property

Example:
The following snippet animates an element's CSS color to 'red' over 4 seconds:
    element.animate({color: 'red'}, 4);

Before this change it was equivalent to writing:
    element.animate({color: 'red'}, {duration: 4, fill: 'forwards'});
The element's CSS color persists as red after the 4 seconds have elapsed.

After this change it is equivalent to writing:
    element.animate({color: 'red'}, {duration: 4, fill: 'none'});
The element's CSS color reverts back to its original value after the 4 seconds have elapsed.