comments: Fix total comments count calculation

[pkvach]

Checklist

• All new and existing tests are passing
• I have added an entry to CHANGES.rst because this is a user-facing change or an important bugfix
• I have written proper commit message(s)
  

What changes does this Pull Request introduce?

Changes to properly count hidden comments when calculating the total number of comments.

• isso/views/comments.py: The calculation of total_replies is modified. Instead of directly assigning the value of reply_counts[root_id] to total_replies, it now calculates the sum of all values in reply_counts if root_id is None, otherwise it assigns the value of reply_counts[root_id].

• isso/js/embed.js: The redundant incrementation of the count variable with comment.total_replies was removed.

• isso/tests/test_comments.py: Several assertions are added to various test cases to check the value of total_replies in the response data.

Why is this necessary?

Fixes #448

Demo

• Before fix

• After fix

[jelmer]

please complete the checklist in the PR template

[pkvach]

Added an entry to CHANGES.rst

[pkvach]

Please make a review of this PR.

[ix5]

Changes itself LGTM.

I found this really hard to review because of the terminologies (some values point are dicts (replies) and others are integers (hidden_replies), the request param parent becomes id in the response, and the meaning/calculation of reply_counts was hard to wrap my head around). The existing code is quite clunky and I'm glad you nevertheless took the time to look into it and fix this longstanding issue @pkvach.

Please fix the two identically-named commits (either squash or split the tests/CHANGES changes into appropriately named commits)

[pkvach]

@ix5
Thank you for the review! You're right, it was a tricky one.
To make things easier to follow, I've reformatted the changes into a single Git commit.

[ix5]

Thanks for squashing, LGTM