Update .travis.yml: added command to install APT package "python-dev"

This build https://travis-ci.org/BruceSherwood/vpython-wx/jobs/11764893 failed because of this, and maybe something else
Update .travis.yml: added command to install APT package "libboost-python-dev"

Build still fails
Update .travis.yml: added command to install APT package "libboost-signals-dev"

Build still fails but is going further
Merge pull request #25 from glarrain/patch-1

Update .travis.yml: added commands to install APT packages