use XLIFF format as a base for i18n for portability instead of php arrays

[Phoscur]

• build XLIFF from the current arrays in language/en by hand or with https://github.com/oyagev/PHP-XLIFF
• check which annotations and attributes of the XLIFF format are going to be used for ugamela
• load XLIFF (in a way like symphony does it?)

Pro

• Not only professional translators can profit of annotations for translation
• XLIFF can be interpreted and thereby reused in other clients (not only PHP)
• Separation of concerns: controller logic and translations don't necessarily need to be coupled

Contra

• Performance (parsing without caching the XLIFF globally)
• Added complexity: any other i18n technique will be more complex than PHP arrays
• Other formats like gettext and .po files might be more recognised by the PHP community currently