Implement XLF dialect specific pre-translation state import

For background see https://confluence.translate5.net/display/MI/TRANSLATE-1643++A+separate+autostatus+pretranslated+is+missing+for+pretranslation

Translate5 is able to import the information if a segment was pre-translated in an external tool before it is imported in translate5. This works currently for SDLXLIFF and native XLF (target state flag).

For the XLF dialects from across and memoQ the implementation is missing.

For across XLF is already defined which values and flags should be used as pre-translated, for memoQ this must be clarified with our memoQ using clients first.