Add json fields and modify generation to use primitive data type

First of all, great job !

I added/modified several things : 

* for json fields:
 
 	- in _config.json : add boolean to manage foreign keys
	 - in json table file : 
	    - index : boolean attribute to set if field is an index
	   - nullable : boolean attribute to set if field is nullable or not
	 - default_value : string to set a default value
	 
* refactor packages : 
	- put Column interface in 'table' package
	- put all wrapper in 'wrapper' package
		- all cursorwrapper classes are in 'cursor' package
		- all selection classes are in 'selection' package
		- all contentvalues classes are in 'contentvalues' package
		
* modify classes Column to java interface which extend BaseColumn
* add a default projection for each Column interface
* modify lot of getter/setter to avoir autoboxing (Integer != int)

This generator is very useful ! I hope my modifications will help
Thanks