remove empty whitespace-only blocks from posts

[1jz]

Issue This PR Addresses

Fixes #1189

Type of Change

• Bugfix: Change which fixes an issue
• New Feature: Change which adds functionality
• Documentation Update: Change which improves documentation
• UI: Change which improves UI

Description

Removes redundant elements wrapping <br> elements and replaces repetitive <br> elements with a single <br>

Also removes empty <p> elements.

[humphd]

Regex to deal with the DOM makes me nervous. Can you not use CSS Selectors for this? The DOM already has a parsing engine built into it without us inventing a new one via regex.

There's a famous StackOverflow answer about the perils of this: https://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags?answertab=active#tab-top

[Metropass]

I know this might be a bit pedantic, but I think we should also check for the 0-dot braille for security reasons. Someone could possibly embed something malicious, and use the character as a means to bypass this check. I'll make a mock function for it