Clean up the project

@jakearchibald I wanted to update the browser logos and [I ended up cleaning up the project](https://cloud.githubusercontent.com/assets/1223565/5143264/f06293ee-7196-11e4-9229-8d41f93fdaf1.gif).

Changes:

* Simplified the build process and remove unneeded files.
* Moved all files required to build the site into `src/`.
* Moved to using the browser logos from https://github.com/alrra/browser-logos, so that the logos are always up to date.
* Maked Travis automatically update the `gh-pages` branch<br>
  (@jakearchibald in order for this to work you need you will need to:
    * [enable Travis for this repository](https://travis-ci.org/profile/jakearchibald)
    * [generate a new secure key](http://docs.travis-ci.com/user/encryption-keys/) based on a [GitHub access `<token>`](https://help.github.com/articles/creating-an-access-token-for-command-line-use/): `travis encrypt -r "jakearchibald/isserviceworkerready
" GH_USER_NAME="Jake Archibald" GH_USER_EMAIL="jaffathecake@gmail.com" GH_TOKEN="<token>"`)

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@jakearchibald Take what you consider usefully and let me know if I need to change anything. :)