POM: use latest imagej-updater, scijava-common

This pins the imagej-updater at 0.6.0 and scijava-common at 2.28.0,
both of which include new features necessary for this project.
Add initial UsageUploadService implementation

This service grabs the statistics from the SciJava UsageService, filters
it for relevant objects -- specifically, those from official update
sites -- transforms the filtered result into a JSON string, and then
uploads it to the ImageJ usage server at http://usage.imagej.net/.