I think i can help you. I Just do it after day of trying. First of all project activity-app looking like separete from the main project. The best idea is to look in /distro/build.xml
in several words first you need to run 'mvn -Pdistro clean install -DskipTests' on main directory, like JOram Barrez said. And secondary go to \modules\activiti-ui\activiti-app and run 'mvn clean install' here to get activiti-app.war
