[CALCITE-513] Support for grouping sets in AggregateProjectMergeRule (Jesus Camacho Rodriguez)

Close apache/incubator-calcite#29
[CALCITE-536] Add @PackageMarker to package-info.java so maven-compiler skips compilation when the sources are unchanged

This is a temporary workaround for https://jira.codehaus.org/browse/MCOMPILER-205.
The proper fix is to generate empty package-info.class in maven-compiler-plugin when package-info.java is "empty"
[CALCITE-540] Create git.properties file only at first build. This saves time in development at a cost of stale git.properties
[CALCITE-539] Avoid rewrite of org-apache-calcite-jdbc.properties
[CALCITE-538] Generate Parser.jj only at first build
[CALCITE-537] Skip overwrite of NOTICE, DEPENDENCIES, and LICENSE files
[CALCITE-541] Update maven-source-plugin to 2.4 to get speedup in jdk 1.8

Old version of maven-source-plugin has "is java.version==1.7" guard check for the usage of 1.7+ features.
New version has proper java.version>=1.7, so it is faster in 1.8