upgrade Bootstrap to 4

[Sagarpreet]

🔜

[gitpod-io]

[Sagarpreet]

Changes done on top of @keshav234156 work:

1. Title module uses new flex properties to center align.
2. Boundaries of many buttons were not visible.
3. Writing code had no css, works fine now.
4. Remove <b> html tags.
5. <i> font-awesome tag CSS was not working, works fine now.

[jywarren]

This looks great! Is it ready for a merge? Thanks, @Sagarpreet !!!

[sagarpreet-chadha]

Yes I have done sanity test of all features, feel free to try in gitpod 😄
We can merge then 👍

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[jywarren]

This is awesome! Great work!