build versioning

This merge request addresses issue #8 (closed).

• specify dacapo.version and dacapo.nickname in dacapo.properties file;
• build versino is dacapo version + git hash; this can be overwritten by cmd args;
• use build.target-jar as output jar name; append build version to jar name.

To do an official build, modify dacapo.version and dacapo.nickname in dacapo.properties file, and pass in -Dbuild.is-official=true.