Revert "Remove voucher migration code."

This reverts commit 61c36521034188200a34fb7a99440b1aed1c2438.
Revert "Move voucher code to separate app."

This reverts commit 92456cf0e19a86a35b034f4f75140bac038cf3c3.
Revert "Rename recurring_donations app to donations."

This reverts commit a9a3b3180988495e960424b5a7ca97d1f421813b.
Revert "Second step to removing OrderItem."

This reverts commit d686f7873772c9ff13b58a3f4342e7ceca3467d8.

Conflicts:
	apps/recurring_donations/management/commands/process_monthly_donations.py
Revert "First step to removing OrderItem."

This reverts commit 69f0b8e219d7051f17c6bd6c9e1c2ff5936e3eee.