Press This metaboxes do not conform to new standard style

[duck_]

See title.

Tag box has a different class compared to the normal post screen so that fixes that mostly. Also updated the toggle background image.

Unfixed:

• the bottom of the box headers appears to have a border issue
• when collapsed it looks as if the boxes do not have rounded bottom corners (not entirely sure)

And anything else that I didn't notice straight away.

[koopersmith]

It still needs a little tweaking, but this should cover most of it.

[nacin]

That'll probably need RTL.

[azaozz]

17757.3 looks good.

[nacin]

Only thing I notice is the persistent underline under the blog title, rather than just on hover.

[nacin]

RTL doesn't need much here at all.

[nacin]

In [18279]:

UI refresh for Press This. props koopersmith, see #17757.

[nacin]

Only thing I see is that 'All Categories' and 'Most Used' should probably be on the right.

[azaozz]

In [18282]:

Press This RTL css fixes, props ocean90, fixes #17757

[azaozz]

In [18283]:

More Press This cleanup and fixes, see #17757