Added option to animate reload changes transitions

This is something I've been doing in my own projects for a while now by using a local modified version. I thought I would be good to share it with others.

This PR adds an option to animate reload transitions. When LiveReload detects changes and reloads CSS a short transition of style changes is applied to all elements right after the reload happens. I find it easier to detect changes and it smoothes the workflow (less jarring).

I have created a pull request in the original [LiveReload repo](https://github.com/livereload/livereload-js/pull/11) a while ago but haven't heard from the author. Judging by the age of other pull requests and the last commit date to that project I don't have high hopes for it to ever make it. And since this project hosts its own version or LR, and is the dependency to other package I use ([grunt-contrib-watch](https://github.com/gruntjs/grunt-contrib-watch)), it would be great to get this merged here first. Later I can create separate PRs for grunt-contrib-watch and [connect-livereload](https://github.com/intesso/connect-livereload) to add options to enable the animation from wherever they are called.

This is animation is off by default so no one will see any difference unless they explicitly enable it.