Add support for Symfony 2.8 and 3 using the new directory structure

[gperdomor]

Hi, i'm using Symfony 2.8 with the new directory structure but many things are missing, like template completion or service completion, etc.

Also, the plugin not work with symfony 3.

As proposal i think you should rename the plugin to "Symfony Plugin" to handle both version (Symfony 2 and Symfony 3) :D

[luchaninov]

+1

[Haehnchen]

change settings until i implement new stucture. see https://knpuniversity.com/screencast/new-in-symfony3/new-dir-structure at ~2min

[Haehnchen]

added path structure and auto configuration for new projects; also thinking of auto enable the plugin later on