[WIP] Add Library Manager

This adds a library manager. Not much at the moment though, it just downloads libraries.
Will fix #143 
recommended to add ```-classpath ./libraries/*``` to the start script

todo: 
- [x] download libraries
- [ ] verify libraries
- [ ] load classes without start script modifications
- [x] enable users to choose their own repos
- [ ] download from another repo if the last one does not work