Make more uses of Jinja templates

[darknao]

We only have 3 html templates for now, but we already have parts of the same code on all of them.

Use the power of templating to refactor those pages and eliminate code duplicates like footer & header. See https://jinja.palletsprojects.com/en/3.0.x/templates/

[subhangi2731]

@darknao can I work on this?

[gridhead]

@subhangi2731, there you go.

[subhangi2731]

@t0xic0der @darknao As I've observed, this needs topbar & footers across all the pages to be consistent with each other, which isn't the case currently. So, this issue can be worked only on merging these two short MRs: #207 #210