ChangeLog: Add header for 1.2.0
ChangeLog: Add header for 1.2.0

It's not yet released, but it's useful to already have the line there
for separating the changes in master.

suutari-ai/shoop,shoopio/shoop,suutari-ai/shoop,shoopio/shoop,suutari-ai/shoop,shoopio/shoop