[4.3] New installer

### What we want?
Newscoop installer should be friendly for newcomers. There is list of main functionalists:
* Check system requirements 

We can use for this Tobias Schultze Requirement class (used in Symfony)

* Install needed vendors (with composer)

User will can click on the button, or do this from console (with instructions).
I was think about small window with composer install command output.

* Create database (standard)
* Put sample data into db

We will need doctrine fixtures or nelmio/alice (https://github.com/nelmio/alice) library.

* Run cron jobs

### How this should work?
For whole process we can use one of micro frameworks (Thanks of this we can add to installer option for downloading whole Newscoop trough internet) for example Silex. For views we can use php templates (it will be small).