Reorder installation steps.

Reorder installation steps -- finish installation of virtualenvwrapper first before continuing with using it.
Remove sourcing `virtualenvwrapper.sh`.

Remove sourcing `virtualenvwrapper.sh` since the shell automatically sources it now.
Use `mkproject` to create the project env and directory.

Since we've set `PROJECT_HOME`, we might as well use it.  `mkproject` creates the virtualenv _and_ the project directory, and sets that project directory as the virtualenv's project.  That means future calls to `workon beginners-blog-for-django-starters` will activate that virtualenv and `cd` to the project directory.
Merge pull request #1 from lemuelf/virtualenvwrapper_project

Use virtualenvwrapper's `mkproject` function