geoserver seeder rework

as the name suggests, this is a total rework. the main change is having tests now and ditching the js part of things. i'm confident ruby can divide floats just as well

note: this has been running in production for a while now and proved to be trustworthy
Have a look at the README, but something like:
`./geoserver_seeder.rb -l layer1 layer2 layer3 ...`