Swap should drop mirroring trigger and add retired mirroring trigger

[nave91]

When we are swapping intermediate table -> main table, we need to:

• Drop mirroring from main to intermediate partitioned table
• Rename main table -> retired table
• Rename intermediate partitioned table -> main table
• Create mirroring from newly partitioned main table -> retired table

All the above should happen within a transaction. Unswap should do the opposite.

[time-less-ness]

All of this looks reasonable.