Use .mw-body in skins

 * This helps Parsoid's output reach parity.

 * Merge in conjunction with
   Vector: Iae873906abcd8b2a986e5f728f0ce207256de770
   MonoBook: I0c889950e618b2afa6332c4c56b5531744526e72

Bug: 38726
Change-Id: Id0228fa839ef80b0b3bfee864e81f2c65963e01b
Merge "Use .mw-body in skins"