Add dependency output for changes and todo lists

Add a --deps option which causes report output to represent a single-parented dependency hierarchy between changes.

e.g.:
| NEW       | https://review.openstack.org/127991 | garyk         | VMware: add tests for spawn wi... 
| NEW       | https://review.openstack.org/128931 | garyk         | VMware: refactor cpu allocatio... 
|   NEW     | https://review.openstack.org/68421  | garyk         | VMWare: get storage policy fro...
|     NEW   | https://review.openstack.org/68539  | sabari        | VMware: use storage policy in ... 

Warning: I haven't tested this on all commands! However, as I've included some consolidation, hopefully the coverage is ok. I expect it to work :)