Consider compiling rocker with `-Werror`

[ldaley]

When digging around, I noticed lots of raw types and other things that the compiler will emit warnings for. Using -Werror would force these to be dealt with.

I'm not sure how to do this with Maven.

[jjlauer]

@alkemist PRs would be mucho appreciated if you wanted to dig around. In parent pom.xml, you can change the javac compiler like so...

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.2</version>
    <configuration>
        <source>${java.version}</source>
        <target>${java.version}</target>
        <compilerArgs>
            <arg>-Werror</arg>
            <arg>-Xlint:all</arg>
        </compilerArgs>
    </configuration>
</plugin>