Self-update composer.phar

Lastest update of the composer.phar file.
Restrain wbs/bootstrap & leafo/lessphp to stable (resolves #14)

Update composer.json to restrain two vendors (wbs/bootstrap and
leafo/lessphp) to stable versions, in order to avoid development bugs
that can appear on the dev-master branches of these repo.

Update composer.lock — please execute "php composer.phar install".
Replace deprecated bootstrap syntax in several files
Add a test in events poster-row to avoid url("null")

That would have generated an error message in the console.
Merge pull request #18 from nxtelevision/update-vendors

Update vendors (resolves #14)