Improvement of language packs editor

Current editor throw errors on any occasion. In Edit With mode, not
displaing new variables so its impossible to even know that they exists
without checking in single mode. I seriously tried to create 1.8
translation but after many attempts i ended up with 2 choices.  Create
translation with notepad or improve editor. Chosed second option and
here it is. Improvements are - increased stability and reliability -
More intuitive - When Edit With, always show all variables from file we
compare to. - When Edit With, preserve less significant variables in
edited file (even if they not exists in compared file). - When Edit
With, show list of files for both language packs. - Intuitive,
automaticaly switch modes to proper one in given situation, create files
on demand ect. - Auto generate credits in edited language files. Its not
super polished yet to the degree where it will start to fly, but its
good start at time when it will be needed.