Python Virtualenv support

[fchorney]

Just wanted to point out that if a user decides to install this on Linux/Mac in a python virtual environment (rather than installing the packages systemwide), the "run_linuxmac.sh" script will fail when trying to install the python packages on the following command: python3 -m pip install --user --upgrade -r requirements.txt
To fix this in this specific instance, I had to get rid of the "--user" flag on the pip command.

One potential way to detect if you are in a virtual env would be to check for the existence of the VIRTUAL_ENV environment variable. So one potential fix could be to detect this and change the command if it exists.