Slight adjustments to Good Job's Filament length counter to make fitting easier.

I've slimed down the base so that the wheel can be fitted and adjusted using a m3 grub screw. I've also added some recesses on the back of the idler for the springs to fit into so that they are less likly to dissappear when fitting. 

The tension screws are now inside the model again to help retain the springs while fitting. 

Good Job has some very good instructions on their page [https://www.printables.com/model/281013-filament-length-counter%2Fcomments](https://www.printables.com/model/281013-filament-length-counter%2Fcomments)