Fixture support for scalikejdbc-play-plugin.

This pull request will add fixture feature to scalikejdbc-play-plugin.

 - Fixture scripts are Plain SQL like play-evolutions.
 - A fixture script have a 'Ups' part and a 'Downs' part like evolutions. 'Ups' are executed on starting and 'Downs' are on stopping.
 - The location for fixture scripts is config/db/fixtures/${dbname}
 - Need to specify fixture scripts in application.conf.

   To use in DEV mode
```
     db.${dbname}.fixtures.dev="insert_data.sql"
```
   To use in TEST mode
```
     db.${dbname}.fixtures.test="insert_data.sql"
```
   Multiple scripts are allowed too.
```
     db.${dbname}.fixtures.dev=[ "insert_data.sql", "insert_additional_data.sql" ]
```
   When specified multiple scripts, Ups part are executed in order. Downs are executed in reverse.