bills html, and growth types are very lame... could I do something more like:
    {% for gt in growth %}
        {% if gt.name == 'Min' %}
            <option value='min'
                {% if bt.which_growth == gt.name %}selected{% endif %}
            >{{'%.2f'|format(bt.ann_growth_min)}}% {{gt.name}}</option>


CALC:
    * if I quit at different times of the financial year, technically the amount I earn will be taxed
    differently, but hard to calc - slides around with tax brackets in future

UI:
    * to allow <yr> total on bill summary, need to re-work annual growth to a drop-down
        - [DONE] mock-up
        - need to change 'which growth' to accommodate new growth models (cpi, override*)
            - [DONE] do this in DB with new table - then don't do crazy pattern matching/making up overrides in the UI code
            - get UI to use bill_growth_types table 
            - get UseGrowth() to use bill_growth_types table

For bills:
    * might need to be able to mark a specific bill as an outlier:
        - so we ignore the data somehow (think Gas is messing with my bills)
        - and even electricity, water, etc. for when we were away in Europe but mostly gas/elec