Better Hiera integration

This adds hash parameters to mysql::server to allow specifying grants, users, and databases to
create automatically, which works nicely with Hiera's automatic parameter lookup functionality. Here's an example of the Hiera config I'm using with this:

```yaml
mysql::server::databases:
   citations_production: { charset: 'utf8' }
   identity_production: { charset: 'utf8' }
   devnet_production: { charset: 'utf8' }

mysql::server::users:
   'citations@localhost':
      password_hash: '*f00'
   'identity@localhost':
      password_hash: '*f00'
   'devnet@localhost':
      password_hash: '*f00'

mysql::server::grants:
   'citations@localhost/citations_production.*':
      user: 'citations@localhost'
      table: 'citations_production.*'
      privileges: ['SELECT', 'INSERT', 'UPDATE', 'DELETE'']
```