Improve internal translations

The whole internal translation of translate5 must be consolidated and reworked.

Problems:

• xlf files are used and not cached, so parsed on each request
• we use partly the xlf approach and partly the approach of having translated json files
  • translated JSON would be the successor of the XLF files
  • no caching would then be needed and usage would be easier in multiple regards
• translations are be fragmented over the whole application
  • data/locales/
  • MODULE/locales/
  • termportal translations
  • instanttranslate translations
  • library/ZfExtended/locales/
  • PLUGIN/locales/
• to get the list of available translations all above directories has to be scanned
  • → expensive
• the current setup of translations goes back to the very first version of translate5 and is outdated in any regards
• this led in combination with current changes to problems (TRANSLATE-3308, TRANSLATE-3387)

This issue should obsolete:

• TRANSLATE-779
• MITTAGQI-67
• TRANSLATE-766

Still the basic ideas how translate5 can be used to translate itself should be adopted from the above issues, and over useful ideas - if any.