modern UI, VM properties & avalon

- ADD: Modern UI for WPF library
- ADD: view model properties for editors and text boxes
- ADD: started to implement syntax definition for AvalonEdit text
editors
saving documents

- ADD: can save documents now
loading documents, fixes and improvements

- ADD: loading documents from files
- FIX: license header
- CHG: code improvements
toolbar buttons and window title

- ADD: logic for current toolbar buttons
- ADD: window title is changed by current opened document file