Use constants for ST_Em values
Use constants for ST_Em values

No need to adapt dmapper/rtftok for this one, as those do not handle
<w:em> ATM.

Change-Id: I88da1d0dae804e3d054b7d4158a81cb64cc4b600

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core