[Style Manager] Save user layout style and keep track « cached » in the browser for later use of Graph4dev app

Feature description

Save specific user layout style and keep track for later use of Graph4dev app, without having to load any style file, style being « cached » within the browser.

Linked to issue #21.

Use cases

If a user has applied some style configuration (ex colors of nodes, stroke size, font size etc) it would be nice to save the entire layout. Once the user reconnects/reuses Graph4dev, the styles he used last time are applied again.