Use a classifier of "mod" during maven resolution

[jpmeyer]

• Added an id of mod to the assembly descriptor file
• Updated the vertx.version property to CR2-SNAPSHOT
• Fixed a typo in the vertx.pullInDeps pom property declaration.

The jpmeyer/vertx-maven-java-module and jpmeyer/vertx-maven-rhino-module projects were created from this archetype.