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 while trying to update older translations to new version. Theyre simply hidden.
It looks not bad when just plaing around, but when someone will try to seriously use it to create translation for 1.8 (especially update older language files with Edit With mode, because its less work) its just impossible.

I seriously tried to create 1.8 translation just now but after many attempts i ended up with 3 choices,
1. Translating from scratch,  - no way too many files and it cant be this way on every update when just fiew variables change.
2. Updating  old translation with notepad (omg...)
3. improve editor so it can do what it should do. - help with translation and editing language files (especially updating older translation to new with Edit With feature).
Chosed third option and here it is.

Improvements are : 
* increased stability and reliability - it does not throw php errors or normal errors on any ocasion.
* When Edit With, always show all variables from file we compare to. (its essential when updating)
* When Edit With, preserve less significant variables in edited file (even if they not exists in compared file, never know if someone dont want to keep them as part of his private moding).
* When Edit With, show list of files for both language packs. (easy to see whats missing ect)
* Intuitive - automaticaly switch modes to proper one in given situation, create files on demand ect.
* Auto generate credits in edited language files.
... and perhaps fiew more i forgot.

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 when 1.8 come out.
Just try to use current version to update old language files to 1.8 and then try out improved version.
Youll see the difference, more than words.

![editwith](https://cloud.githubusercontent.com/assets/3224132/3853548/cdfe6224-1ec6-11e4-9cbb-bdb96651a34b.jpg)
Some Examples of enchanced language editor.
You can see on picture which files are missing and whats goin on, (missing files can also be auto created on save)

![fields](https://cloud.githubusercontent.com/assets/3224132/3853625/d259bf56-1ec8-11e4-95f8-ddbe04f9e347.jpg)
In enchanced language editor, you can actualy see new variables that was added in update so you can easly update your translation.
In not enchanced editor, these variables are not even show so user dont even know there was something added and should be translated.

Theres also another enchantement to editor where Edit With text boxes are 'locked' instead of 'disabled' so its easy to copy paste links and other parts from source language pack,
however this is not yet implemented in this version since it require another change first
which is - extend options in generate_text_area #1131