Allow WIP migrations.

While working on a new migration, it is annoying to have to drop and reapply a migration.

Proposed Solution: Consider migrations with `WIP` in their name, they will be applied, but **they won't be recorded to the migrations table**. This allows a single command `ley up` to reapply WIP migrations.

Start by locating the migration application and migrations-table recording flow in the repository, then trace how `ley up` decides which migrations to run. Done means migrations with `WIP` in their names are applied but not recorded, so a later `ley up` reapplies them.

Written by the indexing model from the issue text.