Start animating from a very small scale.

This should actually fix the "flickering".

Decided to leave `opacity` transition, because it's softens the disappearance of `.thumb-overlay` (we can't animate `:hover` class when it's not there, i.e. it just ends abruptly when cursor leaves the `.thumb` tile), although it seems to only work this way with Firefox.

Props to @ZDesign, his pull request #23 prompted me to find another way to solve this.

At the end of the day I'm not really sure what causes it to essentially drop `transform` rules (or make them normal, i.e. scale element to 100% instead of 0%) and [the spec is still pretty much unreadable](http://dev.w3.org/csswg/css-transforms/), so I just tried to get away from extreme values.