Backend: added a class to handle ranges.

This will be essentially useful for ranges manipulation within the context of nodes (graphs).
Many changes (see full description).

- Cleaned the external STD module: removed unused elements and began translating LS to JS
- Moved the graph visualizer a level up (public) folder for more consistency
- Aligned the graph vizualizer application to the latest changes of the backend
- Updated core code: dop, oop, ...
- Updated core business code: mode, node, highlighting, ...
local code
test commit for local hard coded test
Refactored code