As per discussions in #gnome-design, draw battery dynamically to display percentage better.
The code is based on this extension: https://gitlab.com/exalm/gnome-shell-extension-dynamic-battery/tree/adwaita
Icons are based on this mockup: https://www.dropbox.com/s/ngr1oe58q3c4b28/Screenshot%20from%202018-06-29%2014-47-24.png?dl=0
Screenshots:
For empty, fully charged and missing states, icons from icon theme are used, so they will need to be updated accordingly. Other icons are bundled.
Marking this as WIP until I resolve the FIXMEs and icons are updated.