Added a Statistics web-api command.
Merge branch 'statisticsOp' of github.com:kelseyishmael/GeoGit into kelseyishmael-statisticsOp

Conflicts:
	src/web/api/src/main/java/org/geogit/web/api/CommandBuilder.java
	src/web/api/src/main/java/org/geogit/web/api/ResponseWriter.java
use CamelCase for inner class name