Add index for repo browsing (in NetBeans or other IDEs)

In order to generate an index, rather than merging this PR, the following steps may be followed:

1. Obtain the latest version of the nexus-indexer-cli from http://repo1.maven.org/maven2/org/sonatype/nexus/nexus-indexer/

2. Execute the indexer command as follows:
export REPODIR=/path/to/rosjava_mvn_repo; java -jar nexus-indexer-cli.jar -r $REPODIR -i $REPODIR/.index -d $REPODIR/.index -n "rosjava_mvn_repo"
(Perhaps change the -n parameter to the preferred name.)

3. This should generate a .index directory which software such as Netbeans will pick up. The index should be regenerated whenever a package is added or changed.