Move the bake template

In CakePHP - the templates match (more or less) the location of where
the rendered output will be put. Match that in the migrations plugin
Merge pull request #33 from cakephp/move-template

Move the bake template
Simplify return statements in MigrationTask
Refactor the method for retrieving the migration name into a helper method
Rename `bake` method to `snapshot`

This more accurately represents what the method actually performs. The shell also no longer generates a snapshot by default.
Clean up initial migration template

- Use the EventManager to load the MigrationHelper in migration bake templates
- Move migration.ctp to initial.ctp
- Properly output values (nulls, booleans, integers)
- Switch from `save()` to `create()` for initial migration template
- Remove up()/down() methods from initial migration template