[feat] Convert the documentation to Read The Docs template

[dhunstack]

Following changes were made in this commit -

• Sphinx's conf.py file was regenerated. Old configuration file is in conf_old.py
• custom.css was added to set sidebar colors
• documentation.rst page was added to serve as the home page for docs. Replaces the old documentation.html.
• Some rst files were modified to reduce the number of sidebar pages