adding option for a poor man's CI, closes #5

Adds a new configuration parameter `autoRefreshInterval`.  The default value of the parameter is `0` which means that the test runner should not auto refresh.  If the parameter is set to a positive number then the test runner will automatically refresh at that interval (in seconds).  The parameter only applies to the `jasmine:bdd` goal and will be ignored by the `jasmine:test` goal.

Example config with auto refresh set to every 5 seconds:
```xml
<plugin>
    <groupId>com.github.searls</groupId>
    <artifactId>jasmine-maven-plugin</artifactId>
    <version>${jasmine-maven-plugin.version}</version>
    <configuration>
        <autoRefreshInterval>5</autoRefreshInterval>
    </configuration>
</plugin>
```

You can also set the refresh interval by command line which might be more useful:
```
mvn jasmine:bdd -Djasmine.autoRefreshInterval=5
```