Merge pull request #24 from guillermo-carrasco/master

Add run tracker script to pm
Merge pull request #27 from guillermo-carrasco/master

run_tracker second round
Merge pull request #28 from guillermo-carrasco/master

A bit of documentation for run_tracker.py
Merge branch 'master' of https://github.com/SciLifeLab/pm
Check for samplesheets_dir config option as well, very important