add shutdown hook to cli app to gracefully shutdown when terminated through CTRL+C/SIGINT
Merge branch 'master' into ctrl_c

Conflicts:
	src/cli/src/main/java/org/geogit/cli/GeogitCLI.java
	src/core/src/main/java/org/geogit/repository/Repository.java
	src/storage/bdbje/src/main/java/org/geogit/storage/bdbje/JEObjectDatabase.java
Merge pull request #597 from groldan/ctrl_c

gracefully handle CTRL+C on the command line