Two small image handling fixes

* Don't add inline styles as people will otherwise start to depend on
  them. We should instead reference generic styles in <head>.

* Don't duplicate vertical alignment on round-trip. This is a temporary
  work-around for bug 49221, but not a full solution to the halign / valign
  mess.

Change-Id: I9ead611033e4acd9fc83a805c0c3f8882e9fe434
Merge "Two small image handling fixes"