GN-1006

[sandroscosta]

• [x] Improve documentation inside SCSS files to understand what the rules are doing and where;
• [x] Reduce clutter and unnecessary overrides;
• [x] Separate concerns. Move utility functions to different files;
• [x] Fix margins and heights on header and footer;
• [x] Tweak the footer font size and display.
• [x] Check the menu resizing issue where it floats to a uncommon position.
• [x] Truncate username display to not go hover a certain number of characters and break the navbar