Added missing dependencies in order to compile the project

With master, after a fresh git clone, a clean local maven cache, jdk8 installed, ./build and compile gives me:

```
Updating {file:/Users/nicolas/Projects/playframework/framework/}SBT-Plugin...
[info] Resolving org.scala-sbt#sbt-launch;0.13.5-M2 ...
[warn] 	::::::::::::::::::::::::::::::::::::::::::::::
[warn] 	::          UNRESOLVED DEPENDENCIES         ::
[warn] 	::::::::::::::::::::::::::::::::::::::::::::::
[warn] 	:: org.slf4j#slf4j-api;1.7.5: configuration not found in org.slf4j#slf4j-api;1.7.5: 'compile'. It was required from org.slf4j#slf4j-simple;1.7.5 compile
[warn] 	:: commons-io#commons-io;2.4: configuration not found in commons-io#commons-io;2.4: 'compile'. It was required from net.sourceforge.htmlunit#htmlunit;2.13 compile
[warn] 	::::::::::::::::::::::::::::::::::::::::::::::
[info] Updating {file:/Users/nicolas/Projects/playframework/framework/}Play-WS...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[warn] 	::::::::::::::::::::::::::::::::::::::::::::::
[warn] 	::          UNRESOLVED DEPENDENCIES         ::
[warn] 	::::::::::::::::::::::::::::::::::::::::::::::
[warn] 	:: commons-logging#commons-logging;1.1.3: configuration not found in commons-logging#commons-logging;1.1.3: 'compile'. It was required from org.apache.httpcomponents#httpclient;4.3.1 compile

```

Adding those dependencies solves the dependency issue.