Refactor Thread View

Changed the XAML for viewing thread posts. I've removed all the views
except full screen. The navigation controls have been moved to the right
side of the posts.

Fixed a bug when changing pages of threads that have already been
viewed.
Fixed page count when thread is one page.
Fix Html Decode for Avatar Titles

It needs to remove the new lines and trim white space after decoding it.
Now I can see my Japanese avatar title again! やった～！(=ﾟωﾟ)ﾉ
Add post height detection for thread post view.

Trying out code to see if we can detect the height of the post block by
counting the new lines in it.
Update Thread post view.