Modularize UML2ES gradle tasks, make version-agnostic

[mhavey]

UML2ES has its own gradle build file, which is meant to supplement the main gradle build of a specific project. Maybe it could be a plugin instead. The main build file can then import that plugin. Also currently the UML2ES build file hardcodes the versions of its dependencies (e.g., DHF, ml-gradle, MLCP). Figure out a better way.