- Fix bug in lcd_control_temperature_menu
- Remove test menu-item left in from multi-line command feature
- Replace literals with translatable strings
- Reduce lcd_preheat code redundancy
- Reduce menu macro redundancy
- Clean up formatting

Include of language_en.h now behind national language.

All "#define MSG_STR_*" now surrounded by #ifndef and #endif.

This won’t reduce the string storage in the end, but it makes the
language files smaller. Also removed remaining unused strings.

* Depending on extruder count, will add menu items for ultralcd to edit
individual PID parameters for each extruder
* Added menu items to each language_xx.h
* Builds OK, but recommend testing with typical LCD

This reverts commit 2b9722f387.

To test/enable, uncomment the #define DELTA_CALIBRATION_MENU in Configuration.h

Breaking up languages.h makes it easier to translate. Using language
codes makes it easier to select a language and sets the naming standard.