Localized setup

[azett]

FlatPress setup should be localized.

Ideas:

• Getting the user's locale via $_SERVER['HTTP_ACCEPT_LANGUAGE'].
• Additionally: Setup shows language select box, so user can override detected language.
• Chosen setup language should then be language setting for the blog itself.

Thanks to Lubomír who came up with the idea!

[azett]

setup.zip by @lludvik. Thank you very much!

2do:

• Find a generic way to get from the accepted language ("de") to the RFC 1766 code of the language file ("de-de").
• Translate language files.
• Add language selectbox to the first step of the installer.