Add DSL for publishing status checks

[mschenke]

pipeline {
    ...
    stages {
        ...
        stage("Build & Test") {
            steps {
                /* 
                 * Will provide status based on stage success/failure with same name as stage 
                 * or provideStatus("Some Status") can be used
                 */
                provideStatus() 
                ...
            }
        }
    }
}