Upgrade to Bootstrap 5. Closes #238

[vtamara]

• Replaces bootstrap-loader with Bootstrap 5 loaded directly with shakapacker
• Updates navigation bar to Bootstrap 5 and changes presentation to make it somehow similar to the Bootstrap 3 version
• Upgrades react-bootstrap to a version that handles Bootstrap 5 and adjusts css
• Footer improved minimally

After this PR, more work is needed in transition from one demo to another (e.g From "React Router" to "Classic"). With this PR the transition redraws full page without style and after applies style, and it is noticeable but it was not noticeable with Bootstrap 3.

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This change is 

[vtamara]

https://user-images.githubusercontent.com/701221/160287805-be0071ed-eeef-4cb1-9f63-214642869261.mp4

[vtamara]

Nice work.

Is this PR ready to merge?

Reviewed 15 of 15 files at r1, all commit messages. Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @vtamara)

client/app/bundles/comments/components/CommentBox/CommentForm/CommentForm.jsx, line 103 at r1 (raw file):

    let ref;
    switch (+this.state.formMode) {

what does this plus do?

IMHO it is ready to merge.

The plus converts from string to integer in case that this.state.formMode is string (for some reason it was string in my case).

[justin808]

@Judahmeek merge?

[justin808]

@vaukalak Please review and merge if CI is passing.

[justin808]

@ahangarha @Judahmeek I think it's worth considering merging this.

[ahangarha]

@vtamara Would you update your PR and resolve conflicts and CI failures?

[ahangarha]

@justin808 Is this still wanted?

[justin808]

see #528