phone 6.x-2.18

A lot of fixes and improvements :
* Added 7-8-9 as prefixes for french phone numbers
* Added some tests / validations of the code
* Correction on labels of country names in various files
* Singapore phone number validation and formatting improvement
* Character length validation taking into account extension numbers
* Greek phone numbers
* Czech phone numbers formatting issue
* International phone number improvement
* Great Britain phone number fix
* South African phone number improvement (formatting, labels, ...)
* Israeli phone number format fix
* Belgium country code taken into account