Added a Maven Plugin to run "Spek" with maven.

Hi,

I found it not easy to run spek from command line, especially when you have a long list of classes and jars to set in classpah. So I've developed a maven plugin to let users to run spek as a maven goal.

- the goal name is : spek
- default phase is  : test

here is an example: 
```XML
            <plugin>
                <groupId>org.spek</groupId>
                <artifactId>spek-maven-plugin</artifactId>
                <version>${project.version}</version>
                <executions>
                    <execution>
                        <!--Default Phase is : Test-->
                        <!--<phase>test</phase>-->
                        <goals>
                            <goal>spek</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <!--Default Package is the project root package-->
                    <!--<packageName></packageName>-->

                    <!--Default is true -->
                    <!--<text>true</text>-->

                    <!--Default is false-->
                    <!--<html>false</html>-->

                    <!--Default is null-->
                    <!--<outputFile></outputFile>-->

                    <!--Default is null-->
                    <!--<cssFile></cssFile>-->
                </configuration>
            </plugin>
```

The "Spec Samples" module now is using this plugin to execute ConsoleSpeks.

PS1: Even though I have commit permission now, but I thought you should decide if this plugin is useful and should be part of project or not.

PS2: If you are wondering why plugin is not written with Kotlin, the answer is because of following code in Mojo:
```java
    @Parameter(defaultValue = "${project}", required = true, readonly = true)
    private MavenProject project;
```
Maven why of handling templates ( ${project} ) is same as Kotlin and I couldn't find a solution to bypass kotlin compiler. 

Cheers,