fix sensitivities.css
fix handling of virtualenv in deploy

The previous version had these lines:

    VIRTUAL_ENV=${VIRTUAL_ENV:-"$SUPPORTDIR/virtualenv"}
    source "$VIRTUAL_ENV/bin/activate"

...which made too easy to inadvertently run deploy under an inappropriate
virtual env.  The current version replaces the two lines above with

    VENV=${VENV:-"$SUPPORTDIR/virtualenv"}
    source "$VENV/bin/activate"

...so that the virtual env used by deploy can still be overridden explicitly at
the command line, but there's much less risk of doing this overriding
inadvertently (through the current environment).
Merge branch 'dev' of github.com:hmslincs/hmslincs into dev
annotate eqn in sensitivities page