Split up languages.h, use ISO codes

Breaking up languages.h makes it easier to translate. Using language
codes makes it easier to select a language and sets the naming standard.
Clean up, move unused to the bottom, add headings
Added example configs for printers from http://tvrrug.org.uk/
Merge pull request #1194 from boelle/Marlin_v1

Added example configs for printers from http://tvrrug.org.uk/
Merge pull request #1192 from thinkyhead/split_language

Split up languages.h. Use ISO language codes.