Enable codejail by default.

The codejail settings are also updated so that tmp files work.

This also allows the codejail process to be able to rm the sandbox users's
temp directory using sudo since it would not have permission otherwise.
Add a changelog message.
Use the unzip function since.

Unarchive is not the right function since it is for transferring archives from the local machine to the remote one.
Merge pull request #1148 from edx/feanil/enable_codejail

Feanil/enable codejail
Merge pull request #1153 from edx/feanil/update_nltk

Use the unzip function since.
Merge pull request #1155 from edx/jarv/fix-default-license

no spaces in default license
adding the option to run on a single ip