Improves Tutorial Bottom Navigation

[mahakbansal2019]

Issue Description

This issue adds bottom navigation to each chapter/section in the tutorial pages.

Fixes #1467

Changes Made

Made changes in the tutorial files by adding a div at the bottom of each .md file. The div adds the link to the 'previous' page and to the 'next' page. I also styled the div in bootstrap.css

Before :

After :

• Please check if the PR fulfills these requirements

• [x] PR is descriptively titled and links the original issue above
• [x] Before/after screenshots (if this is a layout change)
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• [x] Context for what motivated the change (if this is a change to some content)

[mahakbansal2019]

@patricoferris Please review this PR Thank you :)