Fixes #1214 Language editor improvement

* editor finds translation issues, new variables, untranslated variables ect, and display appropriate info on files list, also highlight these variables while in edit mode.
* added support for RTL languages when editing (behavior can be controlled by CSS classes langeditor_rtl and langeditor_rtl in config_css)
* removed hardcoded html and added css classes to allow editor styling.
* checked and fixed various vulnerabilities, improved backward compatibility with php 5.3 and overall stability.
Merge pull request #1218 from avril-gh/#1214-ACP-language-editor-improved

#1214 ACP language editor improved