Handled error page in books buy, added error page

[c99SRS]

Fixes #(issue number)

#250

Describe the changes you've made

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Added error page, handled error while buying books

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Describe if there is any unusual behaviour of your code(Write NA if there isn't)

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NA

Additional context (OPTIONAL)

You can also configure this error page while configuring it in NGINX.

Test plan (OPTIONAL)

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Checklist

• [250 ] I have mentioned related issue number in PR description.
• I have added screenshots and related demo links of my changes..
• The title of my pull request is a short description of the requested changes.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• Open Source Program names(OPTIONAL: If you participated in any open-source program then please mention the program name here)

[QAZIMAAZARSHAD]

@c99SRS go through the entire website and replace the dummy page with error.html.

and add hyperlinks to the error page wherever it is required.

[c99SRS]

Sure @QAZIMAAZARSHAD

[c99SRS]

HI @QAZIMAAZARSHAD I have updated all the dummy pages with an error pages. please review it and merge it