Add unit tests

[chadrien]

[backported from #9]

Disclaimer: this PR depends on #8

Our company planned to do a fix for Magento URL rewrite bug as well (we even started to write a module) and then we were pointed to this module which does the same and even better!

So we backported the unit tests we wrote to this module to be able to monitor regressions and Magento versions compatibility.

For now the tests only work with Magento >= 1.9.0.0, we have no idea why. The problem seems to come from 2 tests: testMagentoCatalogURLsAreInfinitlyCreatedOnReindex and testIfAnExistingProductChangeURLKeyToAnExistingOneNoExtraURLRewriteIsCreatedOnMultipleReindex. But at least it works for some versions and we hope that now that we share our work with you, maybe someone from the community will have a hint on what's wrong :smile:

Other small changes are:

an .editorconfig file, to ensure every contributor will use the same coding standards a composer.json file to define the tests dependencies and also to be able to publish the module either on http://packagist.org or http://packages.firegento.com and be able to install it with composer