Revert "Revert "Add new recentchanges field rc_source to replace rc_type""

This reverts commit 113f49bb21487f813548fa4e75ecb568c433ecbf after the
schema change has been completed.

Change-Id: I5412466444526986e1209d0982dd62cd5b387ad1
Merge "Revert "Revert "Add new recentchanges field rc_source to replace rc_type"""