Improve code/comment/output markings & display consistency

This PR aims to increase the consistency across the docs for
code blocks and code/comment/output markings.

Rule followed here is "what's visible on the screen should be reflected"

Issue:

 - Docs had various code blocks showing: comments, commands & outputs.
 - All three of these items were inconsistently marked.

Some examples as to how this PR aims to introduce improvements:

1. Removed `> ` from in front of the "outputs". Eg,
`    > REPOSITORY                 TAG       ID              CREATED` replaced with:
`    REPOSITORY                 TAG       ID              CREATED`.

2. Introduced `$` for commands. Eg,
`    sudo chkconfig docker on` replaced with:
`    $ sudo chkconfig docker on`

3. Comments:
`    > # ` replaced with:
`    # `.

> Please note:
> Due to a vast amount of items reviewed and changed for this PR, there
> might be some individually incorrect replacements OR patterns of incorrect
> replacements. This PR needs to be reviewed and if there is anything missing,
> it should be improved or amended.

Closes:
https://github.com/dotcloud/docker/issues/5286

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)