Create basic posting and thread pages

[rafalp]

It took me 40 days to do new threads lists, and those are still not completely finished. If I am going to follow this approach to posting and thread views, its going to take me another 80 days.

Instead I would like to use an alternative approach to those and first implement very basic versions for them, and then improve them in multiple small iterations. That way I could have many small PRs instead of two gigantozauric PRs.

TODO

• Start new thread
• Read thread contents
• Reply to a thread
• Edit a reply in a thread
• Upload/remove attachments

[rafalp]

Because those changes should also include new parser, I will roll in new minimal posting form and new minimal threads pages together as one PR.

[rafalp]

I've instead merged minimal thread posting view first. Now I'll do minimal thread views. Those minimal thread views will check user permission to see a thread and will display to them a thread with paginated posts list. Reply/edit/moderation/etc will happen as separate extra PRs.

[rafalp]

I will keep this open until minimal thread view lets users post new replies and edit existing ones.