Dependency downloader implementation

This is dependency downloader for scala. based on code from @anthonycorbacho , Pull request https://github.com/Leemoonsoo/zeppelin/pull/2 

I correctly implemented where class load into scala compiler.
Other codes remain the same. only with tiny refactoring.

to verify, try
```
dep.load("com.maxmind.geoip:geoip-api:1.2.14")
import com.maxmind.geoip._
```

Ready to be merged.