Fix post content styling capability and control

Currently the way the parser breaks out the content for the post it breaks everything up by line breaks. This is a very bad practice as it provides no control to the theme author on the content. Furthermore there are several places through out the BBCODE/parser that use the wrong way of rendering certain elements and also could provide slightly better control via classes rather than inline styles

https://area51.phpbb.com/phpBB/viewtopic.php?f=81&t=51586

Goals:
1. Give everything the correct semantic tags.
2. Provide classes over inline styles for better control everywhere, also for better consistency
3. Fix the way line breaks are handled and instead prefer paragraphs as it was in 3.1
4. Use a better class naming scheme that follows the practices of the new theme to avoid over-qualifying/specificity issues.