add migrate old number migrations option

When team develop on git

* Developer A add migration 010_a to branch A
* Developer B add migration 010_b and 011_b to branch B
* Developer C add migration 009_c to branch C
* Branch A merge to master and ``oil r migrate``.
    * master migrations: 001..008 and 010_a
* Branch B merge to master and ``oil r migrate``.
    * master migrations: 001..008, 010_a 010_b and 011_b
    * 010_b is skipped migration
    * because 010 is migrated yet.
* Branch C merge to master and ``oil r migrate``
    * master migrations: 001..008, 010_a, 010_b, 011_b and 009_c
    * 009_c is skipped migration
    * because 009 is less than current number

I fix these

* migrate same number
* add migrate old numbers option