Reorganized setup.py code
Added "deb" setup command
more reorganization to make setup-helpers code more generic
Updated build system to use pybuild
- now generates python-pyqtgraph, python3-pyqtgraph, and python-pyqtgraph-doc packages
- `python setup.py sdist deb` works
remove tools/debian; will add a new branch with debian/ at the root.
copy setHelpers.py changes from debian/ branch
Merge branch 'deb_build' into develop

- removes the tools/debian directory (re-added in debian branch)
- updates to setup scripts