Uses new API features for preview, deleting, pinning, and closing. Refactors and improves styling to match new mockups.
Adds the new post filter bar element.
This adds a major chunk of UI code to the application covering topic listing,
topic filtering, subtopic browsing, browsing posts by topic, filtering unread
posts, filtering followed posts, sorting posts by recent activity, most activty
and most votes, liking/unliking a post, following/unfollowing a post, listing
comments and replis in a post.
Co-authored-by: Kshitij Sobti <kshitij@sobti.in>
