re #28 add language_id attribute in SellerUser model
re #fix_28 set language_id for all the created seller user in the
database initialization script
re #28 set the selected default option in the language select box
re #28 update the user properties template to set by default the current
user selected language in the languages select box
Merge pull request #52 from jean553/fix_28C

Fix 28 c - SellerUser settings - Set default language to the current seller user language