posts: fix "Resize to window" for ugoira

[hdk5]

There are three things incorrect as of now:

First, Note.Box.scale_all, which is supposed to adjust font size for embedded notes, applied it to the whole image/notes container, which also contained ugoira controls, making them incorrectly sized, and the image itself, giving it a large top padding. The fix is to change font-size only for .note-box elements.

Second, Post.resize_ugoira_controls couldn't calculate the right slider width - it was trying to use the image's width, but the image itself adjusted own width to match slider. The fix is to get rid of that function and just use CSS.

[hdk5]

A minor annoyance (that doesn't bother me enough to fix): the slider width jumps on play/pause due to the button not being constantly sized:

On current version, however, the slider itself jumps right/left: