Add support of Jinja2 in script commands

Currently provide cluster, job and base_url as variables.
Fix typo script => scripts
Don't specify number of slots on qsub

Allow the number of slots to be specified in the script. The
number_of_slots variable will be templated.
Use cluster_user rather than hardcoding user
Merge pull request #51 from cjh1/templating

Templating