add locale support

[codekidX]

adding locale support is a tedious task by hand but rubik has its own config management system to leverage from.

idea is:

• config/locale/{langabbr}.toml can be the language specific configutaration used.
• language struct declaration can be inside config/lang.go
• headers to pick up from can be lang
• default language can be set from config using lang top level field
• and a new type of transport key called locale can be introduced to inject language specific configurations

Code:

type MyEntity struct {
  Locale LocaleConfig `rubik:"|locale"`
}