Refactor search to use react

[mattheu]

Refactor existing search component to use React.

Not sure why I didn't write it like this to begin with. I think it was because I wasn't sure about using react to augment an existing component. However I think it's nice to keep the code in the theme a bit more consitent and its much neater now.

Couple of queries.

• The live search is so fast my spinner is barely visible. Do people think its useful? I tried to debounce the removal to make the transition a little less frequent.
• The result items need the width of the container. This is to make the animation smoother. I've passed this in as a property, but doesn't really feel like a nice use of properties.

[pdewouters]

Just a few comments, might be worth considering this library for the class name logic https://github.com/JedWatson/classnames

I usually use const for declaring variables that won't get reassigned, and let in other cases

[mattheu]

Thanks for your review. Some good pointers on ES6. And I think the className library could be useful.

[mattheu]

Think i've hit all of these things. I'm going to go ahead and merge!