Add basic support for optional region-codes

[twiro]

While I don't want to change the way this extension manages and uses languages in the backend (2-character ISO 639-1-codes) I'm planning to add some basic support for optional region-codes in the frontend. All methods explained in the language detection stack (except the fallback language) should be able to include an optional region-code that's accepted, understood and processed by the extension - meaning the extension will extract the 2-character language-code, use that like before and simply add the optional region-code to the parameter pool for individual usage in the templates.

An example of different url-structures that are planned to be supported:

• domain.com/page/?language=en
• domain.com/page/?language=en&region=us
• domain.com/en/page/
• domain.com/en-us/page/
• en.domain.com/page/
• en-us.domain.com/page/