[build] (change:major) Major changes to build.xml in order to improve modularization and jar size reduction. Now rain.jar only contains core classes (i.e., the ones that are workload-aware). The workload-aware classes, along with their third-party dependencies are confined to the related workload JAR file. This also should improve maintanability and dependency problem since two or more workloads are not forced to use the same version of a given third-party library.