Fix ClassCastException on SLF4J and LogBack

This PR fixes the exception you get, when you run the app on the ```master``` branch.

It was caused by us using ```JoranConfigurator``` and ```slf4j-simple.jar```. The fix is to not use the ```slf4j-simple.jar``` and use the ```slf4j-api.jar```

```
INFO: Initializing c3p0-0.9.1.2 [built 21-May-2007 15:04:56; debug? true; trace: 10]
575 [main] ERROR org.scalatra.servlet.ScalatraListener - Failed to initialize scalatra application at
java.lang.ClassCastException: org.slf4j.impl.SimpleLoggerFactory cannot be cast to ch.qos.logback.classic.LoggerContext
	at ScalatraBootstrap.configLog(ScalatraBootstrap.scala:56)
	at ScalatraBootstrap.init(ScalatraBootstrap.scala:27)
	at org.scalatra.servlet.ScalatraListener.configureCycleClass(ScalatraListener.scala:67)
	at org.scalatra.servlet.ScalatraListener.contextInitialized(ScalatraListener.scala:23)
	at org.eclipse.jetty.server.handler.ContextHandler.callContextInitialized(ContextHandler.java:798)
	at org.eclipse.jetty.servlet.ServletContextHandler.callContextInitialized(ServletContextHandler.java:444)
	at org.eclipse.jetty.server.handler.ContextHandler.startContext(ContextHandler.java:789)
	at org.eclipse.jetty.servlet.ServletContextHandler.startContext(ServletContextHandler.java:294)
	at org.eclipse.jetty.webapp.WebAppContext.startWebapp(WebAppContext.java:1341)
	at org.eclipse.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1334)
	at org.eclipse.jetty.server.handler.ContextHandler.doStart(ContextHandler.java:741)
	at org.eclipse.jetty.webapp.WebAppContext.doStart(WebAppContext.java:497)
	at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:68)
	at org.eclipse.jetty.util.component.ContainerLifeCycle.start(ContainerLifeCycle.java:132)
	at org.eclipse.jetty.server.Server.start(Server.java:387)
	at org.eclipse.jetty.util.component.ContainerLifeCycle.doStart(ContainerLifeCycle.java:114)
	at org.eclipse.jetty.server.handler.AbstractHandler.doStart(AbstractHandler.java:61)
	at org.eclipse.jetty.server.Server.doStart(Server.java:354)
	at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:68)
```