chore: add size tracking for deliverables - part 1

In the spirit of "what gets measured gets managed" here is the first part of the size-tracking infrastructure for #space deliverable. This little script will, for now, print out pretty table with file sizes (only when the build is successful). 

Next steps are:
* push results to some (on-line) repository (mongolab?)
* hook it up with GitHub PRs system to have a bot reporting back on GH like coveralls, travis etc.
Could it be made generic so that it is done on all files in `dist` folder please?