apply compileGwt on jar project

[gesellix]

Enhance example-library to show how the compileGwt task can depend on the jar task and how the resulting jar file can be modified to contain the gwt compile output.

closes #12

[steffenschaefer]

Thank you for the PR! As described in #12 the library example is simply a library (widget library) and won't have GWT compilation functionality in the future.

[steffenschaefer]

One additional note: If you configure the jar task this way you will get a jar that contains your classes as well as the GWT compiler output. I personally would create a separate jar or zip task that only packs the GWT compiler output. If you want to upload this to a maven repository you can simply use a special qualifier (e.g. gwt). Then you have 2 jars, one with the classes and one with the compiled GWT stuff.

  task gwtJar(type: Jar) {
    dependsOn compileGwt
    from(compileGwt.outputs) {
      exclude '**/WEB-INF/**'
    }
  }

  publishing {
      publications {
          mavenJava(MavenPublication) {
              from components.java
              artifact gwtJar {
                  classifier "gwt"
              }
          }
      }
  }