Prestashop version 1.4

**WARNING**
During installation module change core files of prestashop installation. 
All actions described in **INSTALL** section and will rollback after uninstalling module

***INSTALL***
1) Copy exfeatures folder content in modules/ directory

2) Go to Prestashop Admin Panel -> Modules -> Front Office Features -> exfeatures -> install

3) During to install walk throught next steps:
	* Creating table _DB_PREFIX_feature_group
	* Creating table _DB_PREFIX_feature_group_lang
	* Adding field 'id_group' to table _DB_PREFIX_feature
	* Adding table 'position' to table _DB_PREFIX_feature
	* Updating _DB_PREFIX_.tab table - class of tab 'Features' change from AdminFeatures to AdminExFetures from exfetures module
	* Update _DB_PREFIX_.tab table - class of tab Catalog change from AdminCatalog to AdminCatalogExFeatures from exfetures module.
		Tabs replacement is one the same, you can do in Employees -> Tabs.
		Intall script of this module do this automatically for you
	* Patch core file <adminFolder>/tabs/AdminCatalog.php
		Do not very worry about this - everything what have been changed is visible of $adminProduct property of AdminCatalog class from private to protected.
		Tests was show, that such replacement not damage system.
	* Copy ajax_ex_features.php to <admin> folder
	* Copy Product.php to /override/classes/_Product.php
	* Patch default (prestashop) theme for display grouped products. 
		File, which should be patched: themes/prestashop/product.tpl. 
		Please, make backups of this files before installing module.
	* Create default group. 
		After installation module, you can see only features, which belong to one of existing groups.
		That's why during installation was created one group with name 'Common' and all features, which exists in system moved in this group
	Everything this you can see into exfetures.php file in install function
	Please click 'configure' to check whether or not module install properly

Architecture notices

During installation module, we copy file Product.php to override/classes/ folder. This script contain class Product, which extends ProductCore class from classes/Product.php
In class Product has overrided method getFetatures, which return features grouped in groups. 

During installation patche file theme/prestashop/product.tpl, 
replace piece of code, which display features on piece of code, 
which take into consideration groups in $features array.

Functional for working with features contains in file AdminFeatures class.
Module contain class AdminExFeatures for adding functional for working with groups too. 
Methods of this class calls because this class become class of tab 'Features' (see exfeatures::install())

Because I want display groups of features in product editing form I also extend AdminCatalog class by AdminCatalogExFeatures class
In this class overrides constructor, where property $adminProducts set in instance of AdminProductsExFetures class.
This class extends AdminProducts class, overrides displayFormFeatures method for displaying features by groups, using two-levels tree/