Move data from app.php to "uploads" directory

Hello,

I've slightly modified the code to read entities (startups, investors, ...) from src/app.php to uploads/{city}/{entity}. This way you don't have to update source code each time a new organization has to be declared but JSON files instead. 
Moreover, at deployment time, you can import uploads/grenoble from one github repository, uploads/lyon from another, ... so you don't have to manage all by yourself but delegate administrations to other users ;)

Merge it if you like, trash it if you don't :)