Schema migration status

This will allow you to run `migrate:status` and see migrations that have already migrated and those which haven't. The code is based on code from https://github.com/davedevelopment/phpmig.

```
$ artisan migrate:status

 Status   Migration Name
--------------------------------------------
   up     2014_05_12_112556_AddUsersTable
  down    2014_06_19_110125_AddGuessTable
   up     2014_06_18_220416_AddOauthTable *** MISSING ***
```