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.