Misc. minor changes.
- Revert back all the changes from doxygen generated CSS file, instead put all the overwritten styles in our own main.less file for easier Doxygen version upgrade in future.
- Add new custom Jekyll include for listing source and binary packages for future Urho3D releases.
- Add "View on GitHub" link to navigation menu on really small viewport when the usual GitHub button links are not displayable.
- Add more icons from font-mfizz.
- Minor tweaks and fixes here and there to make documentation viewing on small viewport becomes easier.
- Add credit orderedlist/minimal team for the web theme in the humans.txt file.