Log script change/add and removal at INFO level

Now that dynamic scripting is disabled, it's extremely helpful to know if/when a script is added or removed via the `ScriptChangesListener`, previously these were only TRACE level messages, they now look like:

```
[2014-05-09 12:01:25,393][INFO ][script                   ] [Plunderer] compiling script file [/Users/hinmanm/src/elasticsearch/config/scripts/calculate-score.mvel]
[2014-05-09 12:02:25,397][INFO ][script                   ] [Plunderer] compiling script file [/Users/hinmanm/src/elasticsearch/config/scripts/test.mvel]
[2014-05-09 12:03:25,399][INFO ][script                   ] [Plunderer] removing script file [/Users/hinmanm/src/elasticsearch/config/scripts/test.mvel]
```

To give an indication as to when the script changes have noticed and the scripts added/reloaded/removed.