Migrate Wiki pages for Installation and Certificate Management into `docs`.

* Added user impersonation and username to ui

* groups working

* Added unit tests, extras for impersonation

* added docs

* fixed formatting to be consistent

* updates per pr review

* ran npm frontend:fix per travis ci

* Add architecture doc
Move images to the new dir

* Add deps managment doc

* Update some of the docs

* Update link to the docs

* Add links to the wiki

* Update 1.6.x-and-below.md

* Update 1.7.x-and-above.md

* Update architecture.md

To migrate wiki contents into `docs/`, prepare directory and file structures.
Contents of each pages would be added as latest in subsequent PRs.