Few fixes and features

This pull request fixes a few things. I suppose styles could be broken since I changed the views a bit to reduce code redundancy.

I believe I fixed issues #561, #443, #592 (already marked closed though) and #569

Besides that, a few unreported issues were fixed by commits
- 1145333536ea58fe031e19cfbbe8473b1e123045 (forum.last_visible_post returned hidden posts)
- cd39afef374ddb45bd15ec9cbc9f7a0c95dece0a (show member post count and member sice)

It's my first contribution to a rails engine, so I'm pretty sure I'm not doing it the right way. Please let me know what needs to change to allow my code to be pulled in.