Add `DEPS_DIR` variable to optionaly set the deps directory

Most poeple use `deps` as their dependency directory in erlang
apps.  I found one customer who used `libs` instead.  This change
makes the deps directory configurable.
Merge branch 'jem-klarna' into 1.3
Add extra options to debuild template
Merge pull request #101 from basho/jem-debuild-extra-options

Add extra options to debuild template
Merge branch '1.3' into develop