added :dp, remote-repo and local-repo contexts

:dp
---
We can declare that can declare deps "à la" sbt (but only mvn ones still →  #33 ):
* include with a '+' or nothing  and exclude deps"
* exclude transitively by starting with a '-'

Jars will be added download to the local repo from the remote repos.
Then the list of paths will be added to spark.jars
Finally, the spark context will be restarted

:local-repo
Update the local repo where jars will be downloaded

:remote-repo
Add a remote repo from where deps will be downloaded

![selfie-0](http://i.imgur.com/Zw1vEA4.png)