Documentation, overview restructuring and lightening
Added: - Overview Widgets documentation - `NetworkHandler` new features documentation. - `Graph` documetation. Modified: - Generalized overview widget elements construction. Fixed: - Unknown references in docs - `DataHandler` pop function removed regardless of whether data was pulled from DH or DB (TODO transition to full db mode). - Moved battery level to icon function to utils because future use in `MainHeader` as well.